Puzzles and brain teasers

Table of Contents

23 Fun Brain Teasers That Will Test Your Genius

Although it isn’t actually a muscle, your brain has a lot in common with your biceps: When you exercise it, it gets stronger. Because your brain can’t run, do yoga, or lift weights, however, you’ve got to find a different way to keep it fit—and brain teasers are just the thing. In fact, in one 2018 study published in the Journal of the American Geriatrics Society, people who did brain teasers and other types of “brain training” reported improvements in mental sharpness and in their ability to execute mundane tasks, like cooking and accounting. Want to see for yourself? Take a stab at the following puzzles that’ll test your genius. At the very least, we can guarantee they’ll keep you entertained!

Question: Among timepieces, sundials have the fewest moving parts…

Which timepiece has the most moving parts?

Answer: An hourglass

It has thousands of grains of sand!

Source: Forbes

Question: Upon taking his car to a hotel, a man immediately declares bankruptcy.

What’s the reasoning?

Answer: He’s playing Monopoly

Source: Forbes

Question: A man is stranded on a riverbank with a wolf, a sheep, and a cabbage…

He finds a raft with which to cross the river, but the raft can fit only himself and either the wolf, the sheep, or the cabbage. If he leaves the wolf with the sheep, the wolf will eat the sheep. If he leaves the sheep with the cabbage, the sheep will eat the cabbage. How can the man cross the river with the wolf, the sheep, and the cabbage?

Answer: The man crosses first with the sheep, leaving the wolf with the cabbage…

He returns alone, then crosses with the wolf, leaving the cabbage behind. He leaves the wolf alone and returns with the sheep. The man leaves the sheep and crosses with the cabbage. He leaves the cabbage with the wolf and crosses one last time, returning with the sheep. Finally, all four are safe on the other side of the river.

Source: Adapted from Icebreaker Ideas

Question: A woman is born in 2020, but dies in 1995.

How can this be?

Answer: The woman was born in 2020 B.C.

Source: Adapted from Reader’s Digest

Question: This five-letter word becomes shorter when you add two letters to it.

iStock

What’s the word?

Answer: Short

Source: Reader’s Digest

Question: A family has two parents and six sons. Each of the sons has one sister.

How many people are in the family?

Answer: Nine

Two parents, six sons, and one daughter!

Source: Reader’s Digest

Question: The water level in a reservoir is low, but doubles every day. It takes 60 days to fill the reservoir.

How long does it take for the reservoir to become half full?

Answer: 59 days

Your first instinct probably is to divide 60 in half. But if the water level doubles every day, the reservoir on any given day was half the size the day prior. If the reservoir is full on day 60, that means it was half full on day 59—not on day 30.

Source: Adapted from Good Housekeeping

Question: How many squares are there?

Puzzles and Riddles

Hint: Don’t forget the big square!

Answer: 40

Count them up here.

Source: Good Housekeeping

Question: In what number parking spot is the car parked?

Puzzler’s World

Hint: There’s a peculiar pattern here.

Answer: 87

Once you realize that you’re reading the numbers upside-down, you’ll see that the car is parked in spot No. 87.

Source: Ranker

Question: You’re in a cabin with no electricity. Come nightfall, you have a candle, a wood stove, and a gas lamp, but only one match.

What do you light first?

Answer: The match

Source: Ranker

Question: In your pocket are two newly minted U.S. coins with a sum of 30 cents. One isn’t a nickel.

What two coins are in your pocket?

Answer: A nickel and a quarter

Only one of the coins is excluded from being a nickel.

Source: Ranker

Question: A cowboy gallops into town on Monday, stays for two days, and leaves town on Monday.

How can this be?

Answer: His horse’s name is Monday

Source: Adapted from Ranker

Question: You’re stuck in a room with three exits…

One exit leads to a pit of venomous snakes. Another exit leads to a lethal inferno. The third and final exit leads to a pool of great white sharks that haven’t eaten for six months. Which door should you choose?

Answer: The third door

Great white sharks typically can only live three months without food.

Source: Adapted from Ranker

Question: What can be found once in a minute, twice in a moment, and never in a thousand years?

Hint: Look closely and you’ll see the answer.

Answer: The letter M

Source: Quora

Question: How far can a squirrel run into the woods?

Hint: Nope, he’s not a particularly fast squirrel.

Answer: Halfway

After that, he’s running back out of the woods.

Source: Icebreaker Ideas

Question: You’re running a race. Before you cross the finish line, you pass the person who is in second place.

In what place did you finish?

Answer: Second place

Source: Good Housekeeping

Question: You need 7 gallons of water, but you only have two jugs with which to measure: a 5-gallon jug and a 3-gallon jug.

How do you measure exactly 7 gallons?

Answer: First, you fill the 5-gallon jug from the faucet…

You then pour the contents of the 5-gallon jug into the 3-gallon jug until the 3-gallon jug is full. That leaves 2 gallons of water in the 5-gallon jug. Next, you dump out the 3-gallon jug and pour the 2 gallons of water from the 5-gallon jug into the empty 3-gallon jug. Finally, fill the 5-gallon jug from the faucet a second time; those 5 gallons plus the 2 gallons in the 3-gallon jug equals 7 gallons.

Source: Icebreaker Ideas

Question: What are the next three letters in the sequence WATNTL?

Hint: The answer’s right there in the question.

Answer: ITS

The complete sequence is the first letter of every word in the sentence.

Source: Icebreaker Ideas

Question: You’re driving a bus. The bus starts out empty…

At the first stop, two people get on. At the second stop, eight people get on and one person gets off. At the third stop, three people get on and five people get off. The bus is yellow, but what color is the bus driver’s hair?

Answer: Whatever color your hair is.

Remember? You’re the bus driver!

Source: Adapted from Icebreaker Ideas

Question: Which word logically comes next in this sequence? Spots, tops, pots, opts…

Hint: Look closely at the letters used to spell each word.

Answer: Stop

All the words are anagrams of each other!

Source: The 125 Best Brain Teasers of All Time

Question: The letters of the word dormitory can be rearranged to produce a two-word phrase that describes a typical dormitory. What is that phrase?

Hint: Think about the words you’d use to describe your child’s dorm room…

Answer: “Dirty room”

…Which is appropriate in this situation.

Source: The 125 Best Brain Teasers of All Time

Question: I have seven billiard balls, one of which weighs less than the other six. Otherwise, they all look exactly the same…

How can I identify the one that weighs less on a balance scale, using that scale no more than two times?

Answer: Separate six of the seven balls into two piles of three and weigh them against each other…

…If the scale balances, then you know that the heavier ball is the seventh remaining ball. If the scale isn’t balanced, then take the heavier side and weigh any two of those three balls against one another. Either the scale will reveal that one of those two balls is the heavier one, or it will balance and reveal that the remaining ball is your culprit.

Source: The 125 Best Brain Teasers of All Time

Question: What is the probability of obtaining either a 6 or a 7 when throwing a pair of dice?

Bet you’re wishing you paid attention in fifth grade math, huh?

Answer: 11/36

The 125 Best Brain Teasers of All Time

To solve this one, start by listing the number of ways to throw either a 6 or a 7. There are 36 possible throws of two dice, because each of the six faces of the first die is matched with any of the six faces of the second one. Of these 36 possible throws, 11 produce either a 6 or a 7. Therefore, the probability of throwing either a 6 or a 7 is 11/36.

Source: The 125 Best Brain Teasers of All Time

How many of these brainteasers, puzzles and optical illusions can you solve?

Today marks the 72nd birthday of Ernő Rubik, the Hungarian professor who invented the mother of all puzzles, the Rubik’s cube.

To celebrate, we thought we’d put together a selection of brainteasers for Mirror Online readers to enjoy.

Have a go at the range of puzzles below – there are nine in total – and let us know how you get on.

1. Spot the T amongst the Ls

Ready, steady, go… (Image: Johns Hopkins University)

How quickly can you spot the T hidden in this collection of Ls?

You might find it quite difficult at first, so we’ll give you a clue… what if we tell you it’s NOT going to be a red letter?

Although this seems like helpful information, scientists have discovered that it can actually slow down your reaction time.

(Image: Johns Hopkins University) poll loading

Did the clue help you find the T?

1000+ VOTES SO FAR

Yes, I think it helped No, it slowed me down

2. Find the Oscar trophy in the crowd of C-3POs

(Image: Mental_floss/Mike Rogalski)

Illustrator Michael Rogalski’s puzzle features a crowd of everyone’s favourite Star Wars droid, C-3PO – but lurking in there somewhere is a golden Oscar statuette.

It’s surprisingly difficult to spot the iconic Academy Awards trophy hidden in the crowd. Have you managed to locate him?

(Image: Mental_floss/Mike Rogalski)

3. Spot the Lego dog amongst the pandas

Can you see it? A Lego Duplo dog is hidden among these pandas (Image: lego/instagram)

Lego posted this puzzle on its Instagram page and captioned it: “We managed to find all the pandas! But can you find our #LEGODUPLO dog.”

4. Find the mobile phone on the rug

A photograph of a mobile phone on a rug went viral on Facebook after infuriated social media users had trouble spotting it – and it’s really stressing them out.

The picture , showing a flowery rug, bears a message telling you to spot the phone and keep it quiet once you’ve seen it.

We’ll admit we were struggling, so we decided to turn to the comments section to cheat a little bit…

Some people had said that if you want to find the mobile, it’s next to the table leg on the right hand side – but that didn’t really help anyway.

Did you find it?

5. How many 3s can you spot on this iPhone?

We’re not sure how or why someone decided to do this, but someone has redesigned this iPhone screen to include a load of 3s.

Guesses have ranged from 10 to 21, with most people saying 19 or 21.

We had a go and counted 19 threes. How many did you get? Let us know in the comments section below.

6. How many girls can you count?

‘Same but different | My entry #whpidentity for @instagram’ (Image: Instagram / tizzia)

Photographer Tiziana Vergari posted the picture as part of an Instagram competition called the Weekend Hashtag Project, for which the theme ‘identity’ was chosen.

There was a great debate in the comments about how many girls are actually in the image, with most guessing either two or four.

Find the mobile phone on the rug

7. Spot the badger

This puzzle, created by BBC Earth, features a badger hidden amongst lots of zebra bums.

(Image: Facebook/BBC Earth)

It’s a little bit weird (and might give you sore eyes) but it’s also infuriatingly difficult.

Give it a go and see how long it takes you before you lose your resolve. Then you can scroll down for the answer.

(Image: BBC Earth)

Did you find him? He’s not so easy to spot, is he?

8. How many triangles are there?

Newsreader, presenter and puzzle-lover Kay Burley posted the tricky problem on Twitter which got people staring hard at the grid and trying to guess.

But there is a way of working out the answer without doing some serious retinal damage.

Kay says the formula needed is 16 + (8×2) + (4×2) + (1×2) + (1×2) to which the answer is 40.

The grid is made up of 16 individual triangles – four in each quarter.

These triangles make up eight bigger one – two in each quarter.

In turn, these form four even bigger ones, which configure two larger ones.

9. Can you solve this brainteaser aimed at children?

Got it? Let’s break it down.

1 apple + 1 apple + 1 apple = 30. So an apple must equal 10 , correct?

1 apple + 4 bananas + 4 bananas = 18. Take away the apple, which we know to equal 10, and you have 8 left. Divide 8 by two to learn the value of a bunch of four bananas, and you have 4. So one banana is equal to 1.

We know that an apple is worth 10 and a bunch of four bananas is worth 4 . Still with us?

Next we are told that if you take away a coconut from a bunch of bananas, you are left with 2. This means that a coconut must equal 2 .

So far, we’ve got it. But it’s the actual sum that people are having problems with – and it’s all down to the coconut.

If you’re adding a coconut to one apple and a bunch of bananas, you’d assume that you’d get 16.

But what people are failing to spot is that there’s only HALF a coconut and three bananas in the sum.

Half of a coconut is 1, and three bananas is worth 3. Add those to your apple (which was 10, in case you’ve forgotten).

We think the answer is 14. Do you agree?

poll loading

What do you think the answer to this brainteaser is?

8000+ VOTES SO FAR

14 15 16 I don’t even know what day it is

Top 25 Programming Puzzles and Brain Teasers

Coding FreakFollow Sep 12, 2018 · 2 min read

Below is the list of top programming puzzles/brain teasers commonly asked in a technical interviews –

  1. Add two numbers without using addition operator | 4 methods
  2. Implement power function without using multiplication and division operators
  3. Swap two numbers without using third variable | 5 methods
  4. Find maximum, minimum of three numbers without using conditional statement and ternary operator | 4 methods
  5. Find numbers represented as sum of two cubes for two different pairs
  6. Multiply two numbers without using multiplication operator or loops
  7. Find square of a number without using multiplication and division operator | 3 methods
  8. Find if a number is even or odd without using any conditional statement
  9. Set both elements of a binary array to 0 in single line
  10. Find minimum number without using conditional statement or ternary operator
  11. Perform Division of two numbers without using division operator
  12. Generate 0 and 1 with 75% and 25% Probability
  13. Generate Desired Random Numbers With Equal Probability
  14. Return 0, 1 and 2 with equal Probability using the specified function
  15. Generate Fair Results from a Biased Coin
  16. Generate numbers from 1 to 7 with equal probability using specified function
  17. Implement Ternary Operator Without Using Conditional Expressions
  18. Determine if two integers are equal without using comparison and arithmetic operators
  19. Return 0 and 1 with equal Probability using the specified function
  20. Clock angle problem — Find angle between hour and minute hand

Thanks for scrolling.

20 Great Brainteasers for Engineers

A lot of tech companies and other employers seem to have a penchant for asking tricky questions for potential candidates to assess how they think. In some cases, there is no right answer per se, it’s rather a way of assessing how your brain is wired. We have “scoured” the internet to find some good examples for you to try. Here are 20 brainteasers for engineers for you to have a go at.

The following are in no particular order and include examples from tech company interviews and classic riddles. There are many, many more out there as you can appreciate. Enjoy.

1. How many zeros?

First on our list of brainteasers for engineers is a cheeky one from Google.

Brainteaser: How many trailing zeros are in the number 5! (5 factorial)?

Answer: 1 trailing zero

Workings: The factorial of 5 is 120. (5 x 4 x 3 x 2 x 1)

Apparently a favorite during an interview for a systems engineer at Google. This is a prime example of a brainteaser geared towards thinking the right way rather than getting it absolutely correct. If you were to calculate it in your mind through brute force, the interviewer would know that. Google suggests it might be easier to think of how many times a ten would be produced doing the sum, rather than the actual correct answer. Apparently, this would be more impressive. Yeah we know, I thought brainteasers were supposed to be fun.

2. Trail by bikes

A cheeky example of brainteasers for engineers from Adobe here.

Brainteaser: There are 50 bikes with a tank that has the capacity to go 100 km. Using these 50 bikes, what is the maximum distance that you can go?

Answer: 350 km

Workings: You might initially think of just making a simple multiplication of the number of bikes and capacities. But remember each has 100 km capacity and they are all in the same place. You could set all 50 bikes off but they’d all only travel 100 km. Now, one solution would be to move all bikes 50 km. Then empty half the bikes’ fuel tanks into the other to fill them up. Keep doing this until you have 1 bike with a full tank to finish the trek. Of course, you’ll have the odd bike stranded when dividing odd numbers. This way you’ll get the last bike of the 50 to have traveled 350 km in total. Nice.

3. To break a bulb

Brainteaser: You have two light bulbs in a 100-story building. You want to find the floor at which the bulbs will break when dropped. Find the floor using the least number of drops.

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This one is from Facebook for the position of a software engineer, though since it’s on the net probably not anymore.

Answer: 16

Workings: You will need to start moving up the building in increments of floors for the first bulb. This could be 10 floors at a time, say. Once you find the point where the first bulb breaks, start again in smaller increments from the last previous incremental floor. So, say you went up in 10-floor increments and it breaks at floor 20, moves back to floor ten with the second bulb. Then start dropping in 1-floor increments. This will give you a worst case of 19. But we can improve on this.

Say you tried floor 16 first. Let’s say it breaks. Go back to floor one and move up in one-floor increments (floors 1-15). This will give you a worst case of 16 drops, if floor 16 was the breaking point, for the second bulb, in the worst case. You can, of course, extend this principle if it doesn’t break at floor 16. You could move to floor 31, 45, 58 etc. for the first bulb etc. Given the use of the same method, you’ll always reach a worst case of 16 drops to find the floor.

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4. Wasting water

This is a classic one and easily applicable as an example of brainteasers for engineers, let’s see if you can figure it out?

Brainteaser: If you had an infinite supply of water and a 5-liter and 3-liter bucket, how would you measure exactly 4 liters? The buckets do not have any intermediate scales.

Answer: A lot of wasted water

Workings: You may already know the answer or have worked it out, but we are obliged to give you an answer. Fill the 5-liter bucket first. Then using that bucket fill the 3-liter bucket being careful not to spill any. This leaves 2 liters in the 5-liter bucket. Now chuck away the water in the 3-liter bucket and refill with the remaining contents of the bigger bucket. Once again fill the 5-liter bucket and fill the second 3-liter bucket. This will leave you 4 liters in the 5-liter bucket. Simples!

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5. Tournament time

Brainteaser: If you had 5,623 participants in a tournament, how many games would need to be played to determine the winner?

One from Amazon for the position of Manager at Amazon. Though it could be applied as an example of brainteasers for engineers.

Answer: Number of participants – 1

Workings: Again another example of the interviewer not looking for the correct answer. They are looking for how you logically think. It would probably be a good idea to get some more information. You could ask “What team sizes are we talking about here?”, for example. Or “Does the number of participants represents the number of teams or individuals?”, so on so forth. If we were to ask directly or assume it was a direct elimination tournament then all teams will lose one game except for the champions. Right? So the answer will be the number of teams -1.

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6. Socks, socks everywhere!

Brainteaser: There are 20 different socks of two types in a drawer in a completely dark room. What is the minimum number of socks you should grab to ensure you have a matching pair?

This example of brainteasers for engineers is (was) apparently for the position of Software Development Engineer in Test at Webtrends.

Answer: 11

Workings: The suggested answer given here is more to show an appreciation of the real world rather than theory, statistics etc. With this in mind, the only way to safely “ensure you have a matching pair” is to pick 11 socks. Those asked by Business Insider said. They say that this is the only foolproof “guaranteed” method of getting a pair in the real world.

7. Parking problems

Brainteaser: The probability of finding the parking slot occupied is 1/3. You find it empty for 9 consecutive days. Find the probability that it will be empty on the 10th day.

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Another one from Google here, according to gineersnow.

Answer: 1/3

Workings: At first this may seem to be a trick question. With probability, you would be forgiven for thinking this, but often it’s not. The fact it’s been empty for 9 consecutive days doesn’t influence the probability of it’s “condition” on the 10th day.

8. Losing your marbles

Brainteaser: Imagine that you have three boxes, one containing two black marbles, one containing two white marbles, and the third, one black marble and one white marble. The boxes were labeled for their contents – BB, WW, BW – but someone has switched the labels so that every box is now incorrectly labeled. You are allowed to take one marble at a time out of any box, without looking inside, and by this process of sampling, you are to determine the contents of all three boxes. What is the smallest number of drawings needed to do this?

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A rather long winded one for the position of Web Technology Intern at Riot Games.

Answer: 1

Workings: Read the question again carefully. The main thing to remember is that the boxes are incorrectly labeled. You can then guarantee the contents of each box with one draw. Let’s say you draw a marble from the box labeled BW. You know this is wrong initially, thus it can only by BB or WW, right? If you draw a white marble you know this box must be WW. That leaves two more unknown boxes. The box labeled BB cannot be BB as the labels are wrong. This must, therefore, be BW. Continue with this logic and you can ascertain the correct label for the last one. “Bada bing”, cool right?

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9. The toss of a coin

Brainteaser: You toss two coins. If you get heads with the first coin, you stop. If you get tails, you toss it again. The second coin is tossed regardless. What is the ratio of heads to tails?

Answer: 1 to 1

Workings: Another probability one here from Amazon. You would expect the odds of heads or tails to be 50/50 for any tossed coin. You would then expect to toss the first coin at least twice. This should, by rights, give you a ratio of 1 to 1. The second coin is continuously tossed and it should also have a ratio of 1 to 1. Hence the ratio of the two must, therefore, also be 1 to 1.

10. Plant your flag

Brainteaser: If you have a square room with no roof, and you had four flagpoles you had to plant on the walls so that each flagpole touched two walls, how would you do it?

This example of brainteasers for engineers is from Cisco from a Software Engineer there.

Answer: Put them in corners dummy

Workings: Yup, you probably go this one off the bat. Plant them in the corners and by virtue, they are touching two walls each. They stated that “I wanted to pierce two walls with a pole horizontally too. They said it was an innovative solution.” Alrighty.

11. Weighing things up

Brainteaser: Given 9 balls all of which weigh the same except for one, what is the minimum of weighings necessary to find the ball that weighs more (or less)?

This example of brainteasers for engineers is brought to you by Business Insider whilst talking to a software engineer at D. E. Shaw and Company.

Answer: 2

Workings: Theoretically you should be able to do this in two weighings, so long as its a two-pan balance. Firstly, take two pairs of three balls and weigh them first. If they balance, you know the “odd” ball is in the last three balls. From that group take two balls and weigh them against each other. Again if they balance it the last one remaining. If however, the first six balls don’t balance grab the set that is lighter or heavier (depending on criteria). In this case, repeat the second step above.

12. Throw it overboard

Brainteaser: You’re in a boat and you throw out a suitcase. Does the water level increase?

Another one from Microsoft here, according to Business Insider.

Answer: Nope

Workings: Water is already being displaced, if you like, by its contributing weight and density to the submerged part of the boat’s hull. So by throwing it overboard, its weight/density will not alter things. If it’s denser than water it will sink and displace its total volume, and if it’s lighter it will displace the portion of its volume dictated by its weight/density. In either case, there will be no change compared to its existing effect on the displacement of the boat prior to being unceremoniously evicted.

13. Buring ropes

Brainteaser: You have 2 pieces of rope, each of which burns from one end to the other in 30 minutes (no matter which end is lit). If different pieces touch, the flame will transfer from one to the other. You cannot assume any rope properties that were not stated. Given only 1 match, can you time 45 minutes?

This cheeky entry on our list brainteasers for engineers comes from an ASIC Verification engineer at Zoran.

Answer: Place one of the ropes at the midpoint between the other and light. Either one rope in a circle or forming a T.

Workings: Depending on the accuracy you are after either solution will work. You could form the first rope into a circle with both ends touching. Then place the other rope, straight, more or less, 180 degrees directly opposite the touching ends. Then light the circular rope touching ends. You could alternatively form a T with one of the ropes bisecting the other at its exact midpoint and light the end of the “vertical” rope, or indeed simultaneously light both ends of the “horizontal” one. In both cases, you get 30 minutes/2 for the circular rope or “horizontal” rope plus 30 minutes for the other rope to give you a total of 45 minutes.

14. Which switch?

Want some more brainteasers for engineers, here’s a fun one.

Brainteaser: In front of you are three light switches. Only one does anything, and it turns on the light downstairs. From here you can’t see the light, and it makes no sound. You must determine which switch operates the light, BUT you can only go check it once. How do you figure out which switch is for the light?

This one comes from a Software engineer at Raytheon.

Answer: 2 switch flicks and a portion of time you can’t get back 🙂

Workings: Light bulbs convert electricity into light and heat right? So, it doesn’t matter which switches you turn on or what order. Try one and wait 5-10 minutes. This should be enough time to make them “hot” if correct. 5-10 minutes should be enough time. If it’s not that one the light will be off and cold right?. Click the second one, it doesn’t matter which so long as it’s not the first one. Again wait another 5-10 minutes. Ok, we are assuming the bulb doesn’t lose all of its “heat” within this time limit.

Now go and check. If the light is on, great you know it’s the second one. It could be off and hot, in this case, it is the first one. If it’s off and cold (assuming it won’t lose its “heat” in the time that’s passed) it’s the last un-flicked one. Or you could trace the wiring, whatever.

15. Bittersweet

Brainteaser: You have 1,000 bottles of juice. One contains poison and tastes bitter. How do you find it in the smallest number of sips?

Answer: 10

Workings: Another one from Microsoft here, apparently. The answer is similar to some of the others on the list, but is about juice so it’s different ok? Take a small sample from 500 of the bottles and take a sip. If it tastes bitter it’s one of those if not it’s the other 500. Then take samples from 250 of the 500 that tasted bitter and keep halving until you find the exact bottle. Easy peasy.

16. Reading in the dark

Bored yet? Shame on you here are some more brainteasers for engineers.

Brainteaser: One night, Aunt Judy was reading a book in the living room. Uncle Jim turned off the light, leaving the room completely dark. Aunt Judy continued to read. How is this possible?

Answer: Aunt Judy is blind and reading in Braille

Workings: A rather simpler one here but fun. We are not told whether Aunt Judy is reading a conventional book, intentionally. Obviously, if she is blind it matters not to her whether the light is on or off. Though we might further question Uncle Jim’s motives. It must be night time is he going to bed? Shouldn’t he be helping her? Of course in our current tablet age, she could also be reading off Kindle. Either way, Uncle Jim needs to reflect on his life 🙂

17. Farmer challenge

Brainteaser: A farmer challenges an engineer, a physicist, and a mathematician to fence off the largest amount of area using the least amount of fence. The engineer made his fence in a circle and said it was the most efficient. The physicist made a long line and said that the length was infinite. Then he said that fencing half of the earth was the best. The mathematician laughed at the others and with his design, beat the others. What did he do?

Answer: The mathematician trolls the other two.

Workings: A fun example of brainteasers for engineers here from TheBrainTeasers, made us chuckle at least. As we know the engineer built a nice circular fence and claimed it was efficient. The physicist decided to make a long line fence of infinite length. He claimed that half the earth should be fenced off for best results. Ok so what about the mathematician? Well, this cheeky chappy decided to build a fence around himself. He then claimed he was the outside of the fence. Nice.

18. Sing us a song

Brainteaser: A man is sitting in a pub feeling rather poor. He sees the man next to him pull a wad of $50 notes out of his wallet. He turns to the rich man and says to him, “I have an amazing talent: I know almost every song that has ever existed.” The rich man laughs.

The poor man says, “I am willing to bet you all the money you have in your wallet that I can sing a genuine song with a lady’s name of your choice in it.” The rich man laughs again and says, “OK, how about my daughter’s name, Joanna Armstrong-Miller?”

The rich man goes home poor. The poor man goes home rich. What song did he sing?

Answer: Happy Birthday to you

Workings: Well not much to add here, pretty self-explanatory.

19. When life gives you lemons

Brainteaser: A bloke in a restaurant decides to challenge a waiter. He asks him to bring a glass, plate, water, a match and a lemon wedge. He then proceeds to pour enough water onto the plate to cover it.

“If you, good sir, can get the water into the glass from the plate without touching or moving it, you’ll get $100”, he challenges the waiter. “You can use all of the items here”.

Shortly after the waiter walks away with the cash. What did he do?

Answer: Create a vacuum in the glass.

Working: Another example of brainteasers for engineers, this one comes from TheBrainTeasers. Perhaps technically more of a demonstration of vacuums than a brainteaser, you could actually try this at home. The answer is to put the match in the lemon slice so it stands vertically on the plate. Then light it and put the glass on it. As the match consumes the oxygen in the glass it will suck the surrounding water into the glass. Hey, presto.

20. Holding water

Finally, we reach the end of our brainteasers for engineers. Still with us? Bravo.

Brainteaser: This object has holes in its top and bottom. It also has holes on its sides and bottom, not only that it is riddled with holes in the middle. Despite this, it can still hold water. What is it?

Answer: A sponge obviously

Workings: A classic one and we don’t think we need to explain this any further.

So there you go, a selection of some interview brainteasers for engineers and classic riddles. Could you answer them all? Good for you. Do you have any favorites you’d like to share?

Via: BusinessInsider, Gineersnow, EngineeringCom, TheBrainTeasers

Consulting Brain Teasers – riddles from real case interviews

Consulting cases can be roughly separated into three categories: business cases, estimating cases and brain teasers. As you can tell by its name, a brain teaser is a riddle or puzzle, which is designed to challenge your logical thinking. Solving brain teasers usually gives the interviewer clues about your potential skill as a future consultant, since combining logic and creative thinking is necessary in order to answer the riddle.

Brain teasers as part of your case interview prep

For most consulting employers it is common practice to use brain teasers as a means for assessing their applicants. The most important aspect for you however, is how you approach the problem, not necessarily giving a specific answer. This will help give your interviewer a clue, as to how successful you might be with actual cases.
You can easily train to successfully solve brain teasers using an analytical approach by practicing the brain teasers in our library.

Practice brain teasers from our library

In order to provide you with the best training possible, we collected brain teasers from our Facebook-Channel for your case interview preparation. These Daily Consulting Brain Teasers will get you ready to land your dream job in consulting.

10 Brainteasers to Stretch Your Brain

Earlier this year, I posted a blog entitled “Tease Your Brain.” It offered 10 brainteasers that showed how our preconceived notions, combined with the brain’s tendency to see what it wants or expects to see, greatly affect how we solve problems and make decisions.

To my amazement, it quickly became one of the most popular blogs I’ve ever posted in terms of the number of hits and reader comments. So in keeping with the Hollywood tradition of following up a huge hit with an even better sequel, here’s another round of brain teasers to test your wits.

1. A man stands on one side of a river, his dog on the other. The man calls his dog, who immediately crosses the river without getting wet and without using a bridge or a boat. How did the dog do it?

2. A sundial has the fewest moving parts of any timepiece. Which has the most?

3. What is unusual about the following words: revive, banana, grammar, voodoo, assess, potato, dresser, uneven?

4. What makes this number unique — 8,549,176,320?

5. Put a coin into an empty bottle and insert a cork into the neck. How can you remove the coin without removing the cork or breaking the bottle?

6. Two boxers are in a match scheduled for 12 rounds. (Pure boxing only – no kicking, UFC takedowns, or anything else). One of the boxers gets knocked out after only six rounds, yet no man throws a punch. How is this possible?

7. In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

8. A man takes his car to a hotel. Upon reaching the hotel, he is immediately declared bankrupt. Why?

9. What do these words have in common: polish, job, herb?

10. You’re standing in a hallway with three light switches on the wall, each of which turns on a different lamp inside a closed room. You can’t see inside the room, and you can’t open the door except to enter the room. You can enter the room only once, and when you do, all the lamps must be turned off. How can you tell which switch turns on which lamp?

***

Ready for the answers?

1. The river was frozen.

2. An hourglass, with thousands of grains of sand.

3. Take the first letter of each word and place it at the end. It will spell the same word backwards.

4. It contains each number, zero through nine, in alphabetical order.

5. Push the cork down into the bottle. Then shake the coin out.

6. Both boxers are female.

7. The person was born in 2005 B.C.

8. The man is playing Monopoly. He lands on a property with a hotel and doesn’t have enough money to pay the rent.

9. All three words are pronounced differently when the first letter is capitalized.

10. Turn on the right switch and leave it on for two minutes. After two minutes, turn on the middle switch and leave it on for one minute. When that minute is up, turn off both switches and enter the room. One light bulb will be hot (1st switch) and one will be warm (2nd switch). The cold bulb will correspond to the switch you didn’t turn on.

How many did you get right?

It doesn’t matter because this isn’t an IQ test. The value lies in stretching your brain beyond its normal ways of thinking. And that can come in handy when trying to innovate and add value to customers in new ways.

To stretch your brain on a regular basis:

  • Put a daily calendar with a puzzle, problem, or poser on your desk. Spend a few minutes each morning trying to figure it out.
  • Post a weekly brainteaser in the company lunchroom or common area. Have fun prizes for the winners – the one who gets it “right” and the one who comes up with the most creative answer.
  • Once a week, read a blog or magazine article that has nothing to do with your industry. Once a month, read a book outside your normal area of interest.
  • Visit a trade show or convention from a very different industry. Focus on what you can learn from that industry that applies to your own.
  • Take a long walk on the beach or in the park and think about nothing at all. Just let the mind wander.

Innovation often comes from seeing what already exists in the world and putting things together in new and different ways. So get out there and stretch those brains; create some new wiring to thrive in today’s hyper paced world! It will be good for you and your business.

Call to action: Forward or retweet this blog to all your friends and have a contest for who gets them the fastest or gets the most ‘right’.

You might also like…

How Many of these 25 Brain Teasers Can You Solve?

1. THE POLE-CLIMBING SLOTH

A slippery sloth climbs six feet up a utility pole during the day, then slides back down five feet during the night. If the pole is 30 feet high and the sloth starts from the ground (zero feet), how many days does it take the sloth to reach the top of the pole?

Answer: 25 days. The math here boils down to a net gain of one foot per day, along with a threshold (24 feet at the beginning of a day) that must be attained so that the sloth can get to the 30-foot mark within a given day. After 24 days and 24 nights, the sloth is 24 feet up. On that 25th day, the sloth scrambles up six feet, attaining the 30-foot top of the pole. Left to the reader is a motivation for the sloth to attempt this feat in the first place. Perhaps there is something tasty atop the pole?

(Adapted from a brain teaser by Carl Proujan.)

2. THE PIRATE RIDDLE

A group of five pirates have to divide up their bounty of 100 coins, as described in the video below. The captain gets to propose a distribution plan, and all five of the pirates vote “yarr” or “nay” on the proposal. If a majority votes “nay,” the captain walks the plank. The pirates are arranged in order, and vote in that order: the captain, Bart, Charlotte, Daniel, and Eliza. If a majority vote “nay” and the captain walks the plank, the captain’s hat goes to Bart, and the process repeats down the line, with a series of proposals, votes, and other acceptance or plank-walking.

How can the captain stay alive, while getting as much gold as possible? (In other words, what is the optimal amount of gold the captain should offer to each pirate, himself included, in his proposal?) Watch the video below for all the rules.

Answer: The captain should propose that he keep 98 coins, distribute one coin each to Charlotte and Eliza, and offer nothing to Bart and Daniel. Bart and Daniel will vote nay, but Charlotte and Eliza have done the math and vote yarr, knowing that the alternative would get them even less booty.

3. THE HIKER’S DILEMMA

A hiker comes across an intersection where three roads cross. He looks for the sign indicating the direction to his destination city. He finds that the pole carrying three city names and arrows pointing to them has fallen. He picks it up, considers it, and pops it back into place, pointing out the correct direction for his destination. How did he do it?

Answer: He knew which city he had just come from. He pointed that arrow back toward his origin point, which oriented the signs properly for his destination and a third city.

(Adapted from a brain teaser by Jan Weaver.)

4. THE PASSCODE RIDDLE

In the video below, the rules of this riddle are laid out. Here’s a snippet: Three team members are imprisoned, and one is allowed the opportunity to escape by facing a challenge. Given perfect logical skills, how can the remaining two team members listen in on what the chosen team member does, and infer the three-digit passcode to get them out?

Answer: The passcode is 2-2-9, for hallway 13.

5. COUNTING BILLS

I had a wad of money in my pocket. I gave half away and of what remained, I spent half. Then, I lost five dollars. That left me with just five bucks. How much money did I start with?

Answer: 40 dollars.

(Adapted from a brain teaser by Charles Booth-Jones.)

6. THE AIRPLANE FUEL RIDDLE

Professor Fukanō plans to circumnavigate the world in his new airplane, as shown in the video below. But the plane’s fuel tank doesn’t hold enough for the trip—in fact, it holds only enough for half the trip. Fukanō has two identical support planes, piloted by his assistants Fugori and Orokana. The planes can transfer fuel in midair, and they must all take off from and land at the same airport on the equator.

How can the three cooperate and share fuel so that Fukanō gets all the way around the world and nobody crashes? (Check the video for more details.)

Answer: All three planes took off at noon, flying west, fully loaded with fuel (180 kiloliters each). At 12:45, each plane has 135 kl remaining. Orokana gives 45 kl to each of the other two planes, then heads back to the airport. At 14:15, Fugori gives another 45 kl to the professor, then heads back to the airport. At 15:00, Orokana flies east, effectively flying toward the professor around the globe. At precisely 16:30, Orokana gives him 45 kl and flips around, now flying alongside the professor. Meanwhile, Fugori takes off and heads for the pair. He meets them at 17:15 and transfers 45 kl to each plane. All three planes now have 45 kl and make it back to the airport.

7. THE HAYSTACK PROBLEM

A farmer has a field with six haystacks in one corner, a third as many in another corner, twice as many in a third corner, and five in the fourth corner. While piling the hay together in the center of the field, the farmer let one of the stacks get scattered all over the field by the wind. How many haystacks did the farmer end up with?

Answer: Just one. The farmer had piled them all up the middle, remember?

(Adapted from a brain teaser by Jan Weaver.)

8. THE THREE ALIENS RIDDLE

In this video riddle, you have crashed landed on a planet with three alien overlords named Tee, Eff, and Arr. There are also three artifacts on the planet, each matching a single alien. To appease the aliens, you need to match up the artifacts with the aliens—but you don’t know which alien is which.

You are allowed to ask three yes-or-no questions, each addressed to any one alien. You can choose to ask the same alien multiple questions, but you don’t have to.

It gets more complex, though, and this wickedly tricky riddle is best explained (both its problem and its solution) by watching the video above.

9. THE FARMER’S WILL

One day, a farmer decided to do some estate planning. He sought to apportion his farmland among his three daughters. He had twin daughters, as well as a younger daughter. His land formed a 9-acre square. He wanted the eldest daughters to get equally sized pieces of land, and the younger daughter to get a smaller piece. How can he divide up the land to accomplish this goal?

Three possible solutions. Chris Higgins

Answer: Shown above are three possible solutions. In each, the box marked 1 is a perfect square for one twin, and the two sections marked 2 combine to make a square of the same size for the second twin. The area marked 3 is a small perfect square for the youngest child.

(Adapted from a brain teaser by Jan Weaver.)

10. COINS

In my hand I have two American coins that are currently minted. Together, they total 55 cents. One isn’t a nickel. What are the coins?

Answer: A nickel and a 50-cent piece. (Lately the U.S. 50-cent piece features John F. Kennedy.)

(Adapted from a brain teaser by Jan Weaver.)

11. THE BRIDGE RIDDLE

A student, a lab assistant, a janitor, and an old man need to cross a bridge to avoid being eaten by zombies, as shown in the video below. The student can cross the bridge in one minute, the lab assistant takes two minutes, the janitor takes five minutes, and the professor takes 10 minutes. The group only has one lantern, which needs to be carried on any trip across. The zombies arrive in 17 minutes, and the bridge can only hold two people at a time. How can you get across in the time allotted, so you can cut the rope bridge and prevent the zombies from stepping on the bridge and/or eating your brains? (See the video for more details!)

Answer: The student and lab assistant go together first, and the student returns, putting three minutes total on the clock. Then, the professor and the janitor take the lantern and cross together, taking 10 minutes, putting the total clock at 13 minutes. The lab assistant grabs the lantern, crosses in two minutes, then the student and lab assistant cross together just in the nick of time—a total of 17 minutes.

12. LITTLE NANCY ETTICOAT

Here’s a nursery rhyme riddle:

Little Nancy Etticoat
In her white petticoat
With a red nose—
The longer she stands
The shorter she grows

Given this rhyme, what is “she?”

Answer: A candle.

(Adapted from a brain teaser by J. Michael Shannon.)

13. THE GREEN-EYED LOGIC PUZZLE

In the green-eyed logic puzzle, there is an island of 100 perfectly logical prisoners who have green eyes—but they don’t know that. They have been trapped on the island since birth, have never seen a mirror, and have never discussed their eye color.

On the island, green-eyed people are allowed to leave, but only if they go alone, at night, to a guard booth, where the guard will examine eye color and either let the person go (green eyes) or throw them in the volcano (non-green eyes). The people don’t know their own eye color; they can never discuss or learn their own eye color; they can only leave at night; and they are given only a single hint when someone from the outside visits the island. That’s a tough life!

One day, a visitor comes to the island. The visitor tells the prisoners: “At least one of you has green eyes.” On the 100th morning after, all the prisoners are gone, all having asked to leave on the night before. How did they figure it out?

Watch the video for a visual explanation of the puzzle and its solution.

Answer: Each person can’t be sure whether they have green eyes. They can only deduce this fact by observing the behavior of the other members of the group. If each person looks at the group and sees 99 others with green eyes, then logically speaking, they must wait 100 nights to give the others opportunities to stay or leave (and for each to make that calculation independently). By the 100th night, using inductive reasoning, the entire group has offered every person in the group an opportunity to leave, and can figure that it’s safe to go.

14. THE NUMBER ROW

The numbers one through 10, below, are listed in an order. What is the rule that causes them to be in this order?

8 5 4 9 1 7 6 10 3 2

(Adapted from a brain teaser by Carl Proujan.)

15. THE COUNTERFEIT COIN PUZZLE

In the video below, you must find a single counterfeit coin among a dozen candidates. You’re allowed the use of a marker (to make notes on the coins, which doesn’t change their weight), and just three uses of a balance scale. How can you find the one counterfeit—which is slightly lighter or heavier than the legitimate coins—among the set?

Answer: First, divide the coins into three equal piles of four. Put one pile on each side of the balance scale. If the sides balance (let’s call this Case 1), all eight of those coins are real and the fake must be in the other pile of four. Mark the legitimate coins with a zero (circle) using your marker, take three of them, and weigh against three of the remaining unmarked coins. If they balance, the remaining unmarked coin is counterfeit. If they don’t, make a different mark (the video above suggests a plus sign for heavier, minus for lighter) on the three new coins on the scale. Test two of these coins on the scale (one on each side)—if they have plus marks, the heavier of those tested will be the fake. If they have minus marks, the lighter is the fake. (If they balance, the coin not tested is the fake.) For Case 2, check out the video.

16. THE ESCALATOR RUNNER

Each step of an escalator is 8 inches taller than the previous step. The total vertical height of the escalator is 20 feet. The escalator moves upward one half step per second. If I step on the lowest step at the moment it is level with the lower floor, and run up at a rate of one step per second, how many steps do I take to reach the upper floor? (Note: Do not include the steps taken to step on and off the escalator.)

Answer: 20 steps. To understand the math, take a period of two seconds. Within that two seconds, I run up two steps on my own power, and the escalator lifts me the height of an extra step, for a total of three steps—this could also be expressed as 3 times 8 inches, or two feet. Therefore, over 20 seconds I reach the upper floor having taken 20 steps.

(Adapted from a brain teaser by Carl Proujan.)

17. A RIVER CROSSING PUZZLE

In the video riddle below, three lions and three wildebeest are stranded on the east bank of a river and need to reach the west. A raft is available, which can carry a maximum of two animals at a time and needs at least one animal onboard to row it across. If the lions ever outnumber the wildebeest on either side of the river (including the animals in the boat if it’s on that side), the lions will eat the wildebeest.

Given these rules, how can all the animals make the crossing and survive?

Answer: There are two optimal solutions. Let’s take one solution first. In the first crossing, one of each animal goes from east to west. In the second crossing, one wildebeest returns from west to east. Then on the third crossing, two lions cross from east to west. One lion returns (west to east). On crossing five, two wildebeest cross from east to west. On crossing six, one lion and one wildebeest return from west to east. On crossing seven, two wildebeest go from east to west. Now all three wildebeest are on the west bank, and the sole lion on the west bank rafts back to the east. From there (crossings eight through eleven), lions simply ferry back and forth, until all the animals make it.

For the other solution, consult the video.

18. THE THREE WATCHES

I am marooned on an island with three watches, all of which were set to the correct time before I got stuck here. One watch is broken and doesn’t run at all. One runs slow, losing one minute every day. The final watch runs fast, gaining one minute every day.

After being marooned for a moment, I begin to worry about timekeeping. Which watch is most likely to show the correct time if I glance at the watches at any particular moment? Which would be least likely to show the correct time?

Answer: We know that the stopped watch must tell the correct time twice a day—every 12 hours. The watch that loses one minute per day will not show the correct time until 720 days into its cycle of time loss (60 minutes in an hour times 12 hours), when it will momentarily be exactly 12 hours behind schedule. Similarly, the watch that gains one minute a day is also wrong until 720 days after its journey into incorrectness, when it will be 12 hours ahead of schedule. Because of this, the watch that doesn’t run at all is most likely to show the correct time. The other two are equally likely to be incorrect.

(Adapted from a brain teaser by Carl Proujan.)

19. EINSTEIN’S RIDDLE

In this riddle, erroneously attributed to Albert Einstein, you’re presented with a series of facts and must deduce one fact that’s not presented. In the case of the video below, a fish has been kidnapped. There are five identical-looking houses in a row (numbered one through five), and one of them contains the fish.

Watch the video for the various bits of information about the occupants of each house, the rules for deducing new information, and figure out where that fish is hiding! (Note: You really need to watch the video to understand this one, and the list of clues is helpful too.)

Answer: The fish is in House 4, where the German lives.

20. MONKEY MATH

Three castaways and a monkey are marooned together on a tropical island. They spend a day collecting a large pile of bananas, numbering between 50 and 100. The castaways agree that the next morning the three of them will divide up the bananas equally among them.

During the night, one of the castaways wakes up. He fears that the others might cheat him, so he takes his one-third share and hides it. Since there is one banana more than a quantity which could be divided equally into thirds, he gives the extra banana to the monkey and goes back to sleep.

Later in the night, a second castaway awakes and repeats the same behavior, plagued by the same fear. Again, he takes one-third of the bananas in the pile and again the quantity is one greater than would allow an even split into thirds, so he hands the extra banana to the monkey and hides his share.

Still later, the final castaway gets up and repeats the exact same procedure, unaware that the other two have already done it. Yet again, he takes a third of the bananas and ends up with one extra, which he gives to the monkey. The monkey is most pleased.

When the castaways meet in the morning to divide the banana loot, they all see that the pile has shrunk considerably, but say nothing—they’re each afraid of admitting their nighttime banana thievery. They divide the remaining bananas three ways, and end up with one extra for the monkey.

Given all this, how many bananas were there in the original pile? (Note: There are no fractional bananas in this problem. We are always dealing with whole bananas.)

Answer: 79. Note that if the pile were bigger, the next possible number that would meet the criteria above would be 160—but that’s outside the scope listed in the second sentence (“between 50 and 100”) of the puzzle.

(Adapted from a brain teaser by Carl Proujan.)

21. THE VIRUS RIDDLE

In the video below, a virus has gotten loose in a lab. The lab is a single story building, built as a 4×4 grid of rooms, for a total of 16 rooms—15 of which are contaminated. (The entrance room is still safe.) There’s an entrance at the northwest corner and an exit at the southeast corner. Only the entrance and exit rooms are connected to the outside. Each room is connected to its adjacent rooms by airlocks. Once you enter a contaminated room, you must pull a self-destruct switch, which destroys the room and the virus within it—as soon as you leave for the next room. You cannot re-enter a room after its switch has been activated.

If you enter via the entrance room and exit via the exit room, how can you be sure to decontaminate the entire lab? What route can you take? See the video for a great visual explanation of the problem and the solution.

Answer: The key lies in the entrance room, which is not contaminated and which you may therefore re-enter after exiting it. If you enter that room, move one room to the east (or the south) and decontaminate it, then re-enter the entrance room and destroy it on your way to the next room. From there, your path becomes clear—you actually have four options to complete the path, which are shown in the video above. (Sketching this one on paper is an easy way to see the routes.)

22. THE IN-LAW CONUNDRUM

According to puzzle book author Carl Proujan, this one was a favorite of author Lewis Carroll.

If the relationships in the prime minister’s family happened to be arranged in the most optimal manner, what would be the minimum possible number of guests be at the party? Note that we should assume that cousin marriages are permitted.

Answer: One. It is possible, through some complex paths in the prime minister’s family, to get the guest list down to one person. Here’s what must be true: The PM’s mother has two brothers. Let’s call them brother 1 and brother 2. The PM also has a brother who married the daughter of brother 1, a cousin. The PM also has a sister who married the son of brother 1. The host himself is married to the daughter of brother 2. Because of all this, brother 1 is the PM’s father’s brother-in-law, the PM’s brother’s father-in-law, the PM’s father-in-law’s brother, and the PM’s brother-in-law’s father. Brother 1 is the sole guest at the party.

(Adapted from a brain teaser by Carl Proujan.)

23. THE PRISONER BOXES RIDDLE

In the video, ten band members have had their musical instruments randomly placed in boxes marked with pictures of musical instruments. Those pictures may or may not match up with the contents.

Each member gets five shots at opening boxes, trying to find their own instrument. Then, they must close the boxes. They’re not allowed to communicate about what they find. If the entire band fails to find their instruments, they’ll all be fired. The odds of them randomly guessing their way through this is one in 1024. But the drummer has an idea that will radically increase their odds of success, to more than 35 percent. What’s his idea?

Answer: The drummer told everyone to first open the box with the picture of their instrument. If their instrument is inside, they’re done. If not, the band member observes what instrument is found, then opens the box with that instrument’s picture on it—and so forth. Watch the video for more on why this works mathematically.

24. S-N-O-W-I-N-G

One snowy morning, Jane awoke to find that her bedroom window was misty with condensation. She drew the word “SNOWING” on it with her finger. Then she crossed out the letter N, turning it into another English word: “SOWING.” She continued this way, removing one letter at a time, until there was just one letter remaining, which is itself a word. What words did Jane make, and in what order?

Answer: Snowing, sowing, owing, wing, win, in, I.

(Adapted from a brain teaser by Martin Gardner.)

25. THE MYSTERY STAMPS

While on vacation on the island of Bima, I visited the post office to send some packages home. The currency on Bima is called the pim, and the postmaster told me that he only had stamps of five different values, though these values are not printed on the stamps. Instead, the stamps have colors.

The stamps were black, red, green, violet, and yellow, in descending order of value. (Thus the black stamps had the highest denomination and yellow the lowest.)

One package required 100 pims worth of stamps, and the postmaster handed me nine stamps: five black stamps, one green stamp, and three violet stamps.

The other two packages required 50 pims worth each; for those, the postmaster handed me two different sets of nine stamps. One set comprised one black stamp and two each of the other colors. The other set was five green stamps, and one each of the other colors.

What would be the smallest number of stamps needed to mail a 50-pim package, and what colors would they be?

Answer: Two black stamps, one red stamp, one green stamp, and one yellow stamp. (It may help to write out the stamp formulas given above using the various b, r, g, v, and y. Because we know that b > r > g > v > y, and we have three described cases, we can do some algebra to arrive at values for each stamp. Black stamps are worth 18 pim, red are worth 9, green are worth 4, violet are worth 2, and yellow are worth 1.)

(Adapted from a brain teaser by Victor Bryant and Ronald Postill.)

Sources: Brain Teasers by Jan Weaver; Brain Teasers & Mind Benders by Charles Booth-Jones; Riddles and More Riddles by J. Michael Shannon; Brain Teasers Galore: Puzzles, Quizzes, and Crosswords from Science World Magazine, edited by Carl Proujan; The Arrow Book of Brain Teasers by Martin Gardner; The Sunday Times Book of Brain Teasers, edited by Victor Bryant and Ronald Postill.

Over the last 2 years we have post­ed close to 100 puz­zles, teasers, rid­dles, and every kind of form of men­tal exer­cise (includ­ing lengthy inter­views with top neuroscientists!).Which ones have proven most stim­u­lat­ing (of the puz­zles and teasers, not the inter­views)? Well, we could answer that ques­tion in a vari­ety of ways, but I’d sug­gest this met­ric: by aver­ag­ing two ranks for each of the brain teasers: the rank for the num­ber of com­ments left, and the rank for total traf­fic received. With­out fur­ther ado…here you have:

Top 15 Brain Teasers and Games for Men­tal Exer­cise

1. Can you count?: Bas­ket­ball atten­tion exper­i­ment (Inter­ac­tive).

2. Which way is the bus head­ing?.

3. Words in your brain: do you know where words are “stored” in your brain?.

4. Please Spot the Dif­fer­ences.

5. Do you think you know the col­ors?: Quick, try the Stroop Test.

6. Clin­i­cal­ly proven Stress Man­age­ment tip.

7. Rid­dle for the Whole Brain: The Blind Beg­gar.

8. What is going on with these pic­tures?.

9. Brain Teasers for the Week­end: a few chal­lenges to exer­cise your atten­tion and work­ing mem­o­ry.

10. Con­sid­er Lin­da’s job prospects: rid­dle, or obvi­ous?.

11. Count the Fs in this sen­tence.

12. Please find the miss­ing num­ber here.

13. How many… exer­cise your Frontal and Pari­etal lobes.

14. Men­tal Imagery and Spa­tial Rota­tion chal­lenge.

15. Enjoy this Sun­day After­noon Quiz.

As a bonus, you can also try and write some Brainy Haikus. To inspire you, below you have a few haikus writ­ten by our read­ers (giv­en that nov­el­ty, vari­ety and chal­lenge are impor­tant for our brains, writ­ing haikus equals ‑for most of us who are not haiku spe­cial­ists- anoth­er form of brain teasers to exer­cise our brains).

– Amit:

Love, col­lege, career.
A new world of tran­si­tions.
Will I sur­vive? Yes.

– Kathy:

My release tech­nique,
For­give, for­get, love all,
Med­i­tate on that!

– Alan:

Through the micro­scope,
slice of brain stains pink and blue,
the won­der of thought.

– Justin:

Justin the genius
Must spell check the word genius
to post this Haiku

– GTB, the skep­tic, says

Haiku’s are easy
But some­times they don’t make sense
Refrig­er­a­tor

Enough?

If you want more brain teasers and games, you can always vis­it our Brain­Teasers page.