Gray's Brain Teasers and Riddles
Please send me submissions to the following collection of brain teasers and riddles.
Collection of quicky teasers.
Marble Contest
Bug Speed
Gold Chains
16 Numbers
Shuffled Decks
Bad Shipping
More Jugs
Two Children
100 Coins
Birthday Ring
Pocket Change
Kids Ages
Balloon in Car
Bananas to Market
Fast Eddie
Passing Ships
Finger Glass
Deep Hole
Water Berries
Rock in Boat
Dropped Cooler
Bird and Trains
Clock Face
Three Advisors
Missing Dollar
Crossing the Bridge
Jugs of Water
Buried in Sand
Einstein Riddle
Student Ages
Ten Bags of Coins
Twelve Balls
Eight Balls
Three Hats
Let's Make a Deal
Quick Puzzles
More Puzzles
Five youngsters entered a contest to guess how many marbles were in a bowl. Alice guessed 45, Betty guessed 39, Chuck guessed 49, Dan guessed 50, and Ed guessed 47. One was off by 6, one by 5, one by 2, and one by 4. One was right.
A caterpillar crawls at a speed of 21cm per hour towards a vegetable patch. After eating its fill it returns, over exactly the same distance, at only 7cm per hour.
Not including the eating time, what is the caterpillar's average speed over the entire journey?
A woman wants to buy something at an auction where you bid grams of gold instead of money. She owns a length of gold chain (with 2 ends) made of 23 interlocking loops, each weighing 1 gram. She wants to go to a jeweler before the auction to cut the minimum number of loops that would allow her to pay any sum from 1 to 23. For example, she could pay a 13 gram price with a 12 link chain and a single link. After much thought, she figures out a way to do it by cutting just 2 of the loops in the chain. How many loops are in the pieces of chains that she has after the 2 cuts?
Below there are sixteen numbers. Assuming that any three of the numbers may be drawn at random, what are the chances that three numbers will be drawn whose sum equals six?
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1
Two identical packs of 52 cards A and B are shuffled thoroughly. One card is picked from A and shuffled with B. The top card from pack A is turned up. If this is the Queen of Hearts, what are the chances that the top card in B will be the King of Hearts?
5 guys who live in apartments make orders from the same company. Unfortunately the shipping company delivered every order to the wrong apartment.
No, you cannot pour some water into the 9 liter jug and then guess. Nor can you fill each jug up half way or something. You have to be exact. A step is defined as pouring water into or out of a jug. For instance, filling the 4 liter jug and then pouring it into the 9 liter jug, and emptying the 9 liter into the pool is 3 steps.
An acquaintance tells you she has two children and you ask her if at least one of them is a boy. She says yes. Assuming every birth has an equal chance of being male or female and you have no additional information about the children, what are the chances that both of her children are male?
What combination of 100 US coins add up to 500 ($5) without using nickels (5 cents). You can use silver dollars (100 cents), 50-cent pieces (50 cents), quarters (25 cents), dimes (10 cents), and pennies (1 cent). If you find one solution, can you find any more?
A man is buying a gold ring set with stones for his wife on her birthday. A ring set with 4 amethysts and 1 diamond comes to US$2,000. One with 3 emeralds, 1 amethyst and 1 diamond would be US$1,400. And one set with 2 rubies and 1 diamond would cost US$3,000. Being a thoughtful husband, he choses a ring with 4 stones, each representing one of their 4 children.
[ Question for people who know the US coins. My apologies to any out of country visitors. ]
You and a friend pass by a standard coin operated vending machine and you decide to get a candy bar. The price is US$0.95 but after checking your pockets you only have a dollar (US$1) and the machine only takes coins.
You turn to your friend and have this conversation.
You: Hey, do you have change for a dollar?
Friend: Let's see... I have 6 US coins but, although they add up to US$1.15, I can't break a dollar.
You: Huh? Can you make change for half a dollar?
Friend: No.
You: How about a quarter?
Friend: Nope. And before you ask I can't make change for a dime or nickel either.
You: Really? And these 6 coins are all US government coins currently in production?
Friend: Yes.
You: Well can you just put your coins into the vending machine and buy me the candy bar, and I'll pay you back?
Friend: Sorry, I'd like to but I can't with the coins I have.
At a party you overhear another guest asking the age of the hosts' 3 children. The host tells the guest that the product of his kids' ages is 72 and the sum of their ages is the same as the guest's house number. Now, the other guest obviously knows her own house number but, after thinking for a bit, she is forced to ask the host for additional information. The host then says that his oldest child likes strawberry ice cream and the other guest is able to say their ages. Even though you don't know the guest's house number, you have enough information.
You're sitting in a car that's not moving with a helium-filled balloon, which is resting up against the car's ceiling somewhere near its middle. The driver hits the gas and the car accelerates forward, throwing you back into your seat.
Fast Eddie the used car salesman sold a well used car for 30% more than it had cost him. The poor soul who bought the car was happy with the vehicle until it started breaking down a week later. The customer who bought the car went back to Fast Eddie and demanded he receive his money back. Eddie countered that the car had been used for a week, thus, no refund. However, Fast Eddie offered to buy the car back for 20% less than the customer paid for it. The customer agreed. Fast Eddie was then able to unload the car for the same amount that he initially paid for it.
A banana grower wants to transport his 3000 bananas 1000 miles across the desert to the market. All he can use is his one camel which can carry 1000 bananas at once but it needs to eat one banana to walk one mile (regardless of how many bananas it is carrying).
You are taking a cruise Liverpool, England to New York City, USA. The passage takes an hour less than 7 days (167 hours) and then the ship is in port 23 hours before returning. The cruise line has ships which depart from NYC and Liverpool every day of the week at precisely 10:00 GMT. The ships all sail along the same route so as you make the passage, you will pass by other ships from the cruise line traveling in the opposite direction.
You have a glass of water sitting on a perfectly balanced scale. You put your finger into the glass and into the water. Your finger does not touch the glass, it only is submerged in the water. It makes the water go higher up the sides of the glass but it does not overflow.
You come across a man digging a deep hole. "How deep is your hole" you ask. He replies "You'll have to guess but I can tell you that I'm 2 meters (200cm) tall". You then say "How much deeper are you going?" He answers, "I am half done. When the hole is done my head will be twice as far below ground as it is now above ground."
You have a large container of berries. When the berries were fresh, 99% of their weight was from the water in the berries. A test 3 days later showed that they had lost some of the water due to drying and were now only 98% water by weight.
You are sitting in a boat floating in a swimming pool. At the bottom of your boat is a heavy rock. You pick up the rock and drop it into water and it immediately sinks to the bottom of the pool.
A guy is paddling a canoe up a stream at a constant speed (through the water). The water is flowing downstream at another constant speed (over ground). At some point a cooler falls out of the canoe into the water. After 10 minutes of paddling the guy notices that it is missing and turns around immediately and paddles downstream. While he is paddling downstream, he travels the same speed through the water as he did upstream. When he finally reaches the cooler, the cooler has traveled 1 kilometer from the spot where it fell out of the canoe.
Two trains are traveling towards each other on separate tracks. They are each traveling at 30kph. When the trains are 1 kilometer apart, a bird leaves one of the trains and flies towards the other at a speed of 120kph. When it reaches the other train it immediately turns around and flies back the other direction. It continues to do this back and forth until the trains reach each other.
You have an analog clock whose face is number in a circle from 1 to 12, with 12 facing "north", 3 "east", 6 "south", and 9 "west". You are allowed to draw two lines which go all the way across the clock face, and divide the numbers on the clock into 3 or 4 groups depending on if the lines intersect. How can you draw the lines so that the numbers in each group add up to the same sum.
A king has three advisors. He wants to find out which of them is the smartest so he devises a test. He tells them that he has 3 white hats and 2 black hats. After seating the three facing each other, he tells them that he would randomly pick 3 hats, which would be placed on their heads so that they could each see only the other two hats, but not their own. Unknown to the advisors, the king tosses away the two black hats and only uses the three white hats. After staring at each other for a while, one of the advisors figures it out and shouts, "I know! My hat is white!" How did the advisor know?
3 men go into a motel. The man behind the desk said the room is US$30, so each man paid US$10 and went to their room.
A while later the man behind the desk realized the room was only US$25, so he sent the bellboy to the 3 guys' room with US$5. On the way, the bellboy couldn't figure out how to split US$5 evenly between 3 men, so he decides to give each man US$1 and kept the other US$2 for himself.
This meant that the 3 men each paid US$9 for the room, which is a total of US$27. Add the US$2 that the bellboy kept brings the total to US$29.
Where is the other dollar!?
Four people are on one side of a bridge that they need to cross. It is dark, there are holes in the bridge surface, and they only have one flashlight which must travel with them as they cross. To add to their troubles, the bridge will only support two people at a time.
No matter how fast a person can cross, he must wait for his companion. If #1 goes with #2, it takes 2 minutes for them to cross. If number #2 goes with #4, it takes them 10 minutes. The flashlight cannot be thrown, instead it must be carried and delivered from person to person. The 4 people are trying to make it across in the fastest possible time to make an important appointment in the next town.
No, you cannot pour some water into the 5 liter container and then guess. Nor can you fill each jug up half way or something. You have to be exact. A step is defined as pouring water into or out of a jug. For instance, filling the 3 liter jug and then pouring it into the 5 liter jug, and then pouring the 5 liter jub into the pool is 3 steps.
A sadistic torturer has buried 3 men up to their necks in sand facing a wall. They cannot turn their heads. #1 is closest to the wall, then #2, and then #3. #1 sees only the wall, #2 can see #1 in front of him, and #3 sees #1 and #2. A hat, either white or black, is put on each man from behind so they cannot see what color of hat they are wearing. It is securely attached so it won't fall off under any circumstances.
Their captor then explains:
How can these men get their freedom?
Einstein supposedly wrote this riddle and said 98% of the world could not solve it. Found on Patrick W. Gilmore jokes page.
There are 5 houses painted in different colors in a row on a street. In each house lives a person with a different nationality. The 5 owners each drink a certain type of beverage, smoke a certain brand of cigar, and keep a certain pet. No owners have the same pet, smoke the same brand of cigar, nor drink the same beverage.
Hints:
There are three switches in a room on the first floor and a lamp on the third floor. Each one is labeled On and Off. One (and only one) of the switches controls the lamp. There is no possible way for you to see whether the light is on or off from the first floor. You are alone in the house.
You overhear a conversation between a professor and his teaching assistant. They are talking about a course they are running with just three students.
So this is a fun one. I think someone sent it to me a while back and I couldn't solve it after spending a lot of time on it. Well I got it again and solved it after an hour or so. I'm sure you can do it faster.
There are (at least) two ways to solve this problem. The first way I solved it is to weigh the balls once, and then make a determination on which balls to weigh next. After I spent some more time on it, the other way to solve it is to configure all of the weighings at the start and look at the results to determine which ball is different and whether heavier or lighter.
I've moved the quicky teasers to a separate page.
Here are some additional puzzle sites I've come across.
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