Classic Short Brain Teasers and Riddles

1. The Exclusive Club

Leslie, Eloise, Bill and Bob belong to an exclusive club. What is it?

See Answer
The club of people whose names can be spelled upside down with a calculator: 317537, 351073, 7718, and 808, respectively.

 

2. Mixing Water and Wine

Water and Wine BucketsYou have a bucket containing one gallon of water and a bucket containing one gallon of wine. You fill a one-cup measuring cup with wine and pour it into the water bucket. You then fill the measuring cup with one cup of the water-wine mixture and pour it back into the wine bucket. At that point, is there more water in the wine, or more wine in the water?

See Answer
The proportions are exactly the same. Because you started with one gallon of water and one gallon of wine, and you now have two one-gallon mixtures, the amount of water that has been transferred to the wine bucket must have been replaced with an equal amount of wine, and vice versa.

 

3. Mixed-up Math

How can 8 + 8 = 4 ?

See Answer
8 a.m. plus 8 hours equals 4 p.m.

 

4. Socks in a Drawer

You have 10 black socks and 10 white socks mixed up loosely in a drawer. You wake up in darkness and only care about having a matching pair, either black or white. Without being able to see the socks, how many do you need to grab to make sure you have a matching pair?

See Answer
Three. If the first two socks are two different colors, the third sock has to match one of them. Often, people’s first instinct is to answer Three, and then they second-guess themselves and say Eleven, which is how many socks you would need to grab to make sure to have a mis-matched pair.

 

5. Shortchanged Hotel Guests

Three guests check into a hotel. They decide to share a room, which they are told will cost $30 for the night. Each guest pays $10 and they go up to their room. However, a short time later, the night manager realizes that she should have only charged them $25 for the room. She therefore gives 5 single dollar bills to the bellhop and tells him to refund the guests’ money. On the way up to the room, the bellhop reasons that there is no way for the three guests to split five dollars evenly, and they are not aware that they are owed a refund anyway, so the bellhop decides to keep $2 for himself, and simply tell the guests that they are each owed a refund of $1. And this he does.

Now, since the 3 guests each paid $10, but they each received a $1 refund, they each actually paid $9, and 9 times 3 equals $27. The bellhop kept $2, and 27 plus 2 is $29. But we started with $30. What happened to the extra dollar?

See Answer
The sum of $29 is arrived at by adding up the wrong things, to create a confusing result. The real math is as follows: of the $30 we started with, each of the guests has $1, making $3, the bellhop has $2, and there is $25 in the register, for a total of $30. Yes, the guests paid $27 total, $25 of it to the register and $2 (involuntarily) to the bellhop.

 

6. The Unexpected Execution

A prisoner has been sentenced to death. The king visits the prisoner’s cell on Saturday, and says, “Your execution will be carried out one day in the week that begins tomorrow. However, I will not tell you the day. In fact, I guarantee that it will be unexpected.”

The prisoner, preoccupied with his fate, tries to determine when the execution will happen. He reasons that it cannot be on Saturday, the last day of the week, because if the first six days have gone by without the execution taking place, then the prisoner will expect it to take place on Saturday, and the king stated that the execution will be unexpected. The prisoner then reasons that the execution cannot happen on Friday either. Since Saturday is an impossibility, that leaves only six possible days. However, if the first five days of the week have gone by with no execution, then the prisoner will expect it on Friday, and the execution is guaranteed to be unexpected. In this way, the prisoner rules out Thursday, Wednesday, Tuesday, Monday and Sunday, and happily concludes that he cannot actually be executed, because there is no way for the day of the execution to be unexpected.

How does the king manage to carry out the execution and still have it be unexpected?

See Answer
He may carry it out on any day of the week he wishes. Since the prisoner has determined that the execution is impossible, he will not be expecting it.

 

7. Too Many Dinner Guests

A hostess has prepared a delicious dinner for eight people. However, a ninth person arrives unexpectedly. There is plenty of food, but only eight chairs. It seems someone will have to stand, until the hostess arrives at an ingenious solution. She seats the first guest and has his girlfriend sit on his lap for a minute. Then the seats the third guest in the second chair, the fourth guest in the third chair, and so on, all around the table, until the eighth guest sits in the seventh chair. Then she simply has the ninth guest get off her boyfriend’s lap and take the eighth chair. Nine guests in eight chairs! At least that’s how she describes it to you. Can you see where the hostess misled you?

See Answer
The girlfriend was not the ninth guest; she was the second. The ninth guest is still standing.

 

8. Splitting the Inheritance

A wealthy matriarch has passed away, leaving a valuable collection of 13 antique vehicles. Her will states that her first-born child will receive half of her collection, her second-born will receive one-third, and her third child will receive one-sixth. The cars may not be sold, but must be divided among the heirs, and if they cannot follow the terms of the will, they get nothing. The three heirs cannot figure out how to split up the vehicles, so they consult with a wise counselor, who comes up with an elegant solution. What does the counselor propose?

See Answer
The counselor takes one vehicle as her fee. The remaining 12 are therefore easy to split up: 6 for the first-born, 4 for the second, and 2 for the third.

 

9. Jugs of Water

You have a 3 liter jug, a 5 liter jug, and a faucet. How can you come up with exactly 4 liters of water?

See Answer
Fill up the 5 liter jug, then pour water from the 5 liter jug into the 3 liter jug until it is full. You now have exactly 2 liters left in the 5 liter jug. Dump out the water in the 3 liter jug, and pour the 2 liters of water from the 5 liter jug into the 3 liter jug. Then fill up the 5 liter jug, and pour water into the 3 liter jug until it is full. You will have exactly 4 liters left in the 5 liter jug.

 

10. A Unique Number

What is unique about 40?

See Answer
It is the only number that, when spelled as a word, has all of its letters in alphabetical order.

 

11. A Unique State Name

What is unique about the word Alaska?

See Answer
It is the only state name that can be typed using just one row of keys on a keyboard.

 

12. The Two Riddles of the Sphinx

Many have heard the Sphinx’s first riddle: What has four legs in the morning, two legs in the afternoon, and three legs in the evening? However, the Sphinx had a second, lesser known riddle: There are two sisters. One gives birth to the other, and she in turn gives birth to the first. What are they?

See Answer to First Riddle
A human being, who crawls as a baby, walks on two legs as an adult, and uses a cane in old age.

 

See Answer to Second Riddle
Day and night.

 

13. Two Ropes

You have two lengths of rope, and you know that each of them will take exactly one hour to burn. However, the rope varies in thickness and some parts may burn at different speeds, so half of a one-hour length may take more or less than half an hour to burn. How can you use the ropes to measure when exactly 45 minutes has elapsed, with no timepieces and without cutting the rope?

See Answer
Light both ends of the first rope and one end of the second rope. When the first rope has burned all the way, 30 minutes has elapsed. Light the other end of the first rope, and when it has burned all the way, another 15 minutes will have elapsed. (Even though parts of the rope may be burning at different rates, when you light both ends, you are still cutting the time in half.)

 

14. Bat and Ball

A bat and a ball cost $1.10 together. The bat costs $1 more than the ball. How much does the ball cost?

See Answer
The ball costs 5 cents. The bat costs $1.05. Many people answer too quickly and say that the ball costs 10 cents. However, if that were true, and the bat costs $1 more than the ball, then the bat would have to cost $1.10, making the total cost $1.20.

 

15. The Stopped Clock

Erika forgot to wind the clock on her wall, so it has stopped, and that is her only timepiece. She walks to a friend’s house to visit, observing the correct time on her friend’s clock while she is there, and then walks home. When she gets home she makes a simple calculation and then sets her clock to the correct time, despite not knowing how long it took her to walk home from her friend’s house. How did  she do it?

See Answer
Before she left her house, Erika wound her clock and set it to 12 o’clock. Therefore, when she returned, she could easily see the total amount of time she had been gone. At her friend’s house, she noted the time when she arrived and when she left, so she knows the amount of time she spent at her friend’s house. She subtracts that from the total time she was gone and divides by two. That is her one-way travel time from her friend’s house, which she adds to the time that was showing on her friend’s clock when she left her friend’s house.

 

16. The Chessboard and Grains of Rice

A great craftsman created a beautiful chessboard for a king, who was so impressed he asked the craftsman to name his price. The craftsman said he wanted to be paid “only a few grains of rice,” in this manner: one grain of rice for the first square on the chessboard, two for the second square, four for the third, eight for the fourth, and so on, doubling the amount for each square up to the 64th square. This did not sound like much, so the king agreed. Was this a good deal for the king?

See Answer
It was not a good deal for the king. This problem illustrates the power of exponential growth. The first row or so of the chessboard would not cause any problems, but for the 21st square the king would have to pay over 1 million grains of rice, and for the 41st square, more than 1 trillion. Total, the king would owe the craftsman 18 446 744 073 709 551 615, or 18 quintillion grains of rice, about 1,000 times the annual global rice harvest.

 

2 thoughts on “Classic Short Brain Teasers and Riddles”

Leave a Comment (it will be moderated and won't appear immediately)

brain teasers, word games, paradoxes, situation puzzles, and optical illusions