Old Chestnut

A puzzle which has been repeated so many times that people who know it groan at hearing it again. This is roughly my criterion for inclusion on this page -- that they make me groan upon re-reading them somewhere -- but as a result, some that are only 10 years old or perhaps newer appear here.

** Note: Most of these links will take you to a node with a more detailed version of the question, but ones marked with bold double asterisks take you directly to an answer node. **

Old chestnuts on Everything:

• Language/word puzzles:
  • ** Two common words in the English language that end in -gry are hungry and angry. Name another. **
  • ** What is the longest English word? **
  • Language equations, like 76 = T. that L. the B. P.
• Date/time puzzles:
  • It's the same time in a west-coast state and an east-coast state of the U.S. How?
  • Two days ago I was 15. Next year I'll be 18. How?
  • How many times in one day do the hour and minute hands of a clock coincide?
  • William is 1/4 Xavier's age. In five years William will be only 1/3 Xavier's age. How old is William now?
• Math/number puzzles:
  • ** What is the next number in the sequence 1, 11, 21, 1211? **
  • If I have two ropes that each burn in one hour, how can I measure 45 minutes?
  • How many times does the digit 9 occur in the numbers 1 to 100?
  • How many zeroes are at the end of 1000! (1000 factorial)?
  • What is the smallest number of U.S. coins which cannot total exactly $1?
  • Monty Hall offers you three doors, reveals one you didn't pick. Should you switch to the third door?
  • Three men fight a pistol duel, taking turns. A always hits his target, B hits half the time, and C hits 3/10 of the time. What is C's best strategy?
  • Three men take a room in a hotel for one night for $30. Later the owner realizes the room actually goes for $25 and sends the bellhop up with their change. . . .
  • Find a ten-digit number using each digit once, with the first two digits forming a number divisible by 2, the first three divisble by 3, etc.
  • There is a row of lockers in a school numbered 1 to N. Students walk by, opening or closing lockers numbered with a multiple of their number. . . .
  • A horseman at the back of a 40 mile army delivers a message to the front, then returns to the back. If the army marched 40 miles in this time, how far did the horse run?
  • You have two identical glasses which will break if dropped from floor N or higher of a 100 floor building, and not break if dropped from a lower floor. What is the smallest number of glass drops with which you can calculate N?
  • You have two unmarked containers which hold exactly five liters and three liters, respectively. How do you measure exactly four liters?
  • How many people do you need to have together in order to have at least a 50% chance of two of them having the same birthday?
  • How can you arrange 15 people into groups of 3 on seven consecutive days so that no two people are in a group together twice?
  • Two bicyclists ride toward each other while a fly flies back and forth between them. How far does the fly fly?
  • Two boats start traveling at different, constant speeds from opposite sides of a river and pass 700 yards from one shore...
• Geometry puzzles:
  • How do you plant ten trees in 5 lines of 4?
  • Connect three houses to each of three utilities without any of the lines crossing.
  • Draw a continuous path that goes through each line segment of some diagram once.
  • Four bugs at the corners of a square walk towards each other. How far do they walk?
  • A man walks 50 miles south from his house, 50 miles west, then 50 miles north and arrives back at his house. How?
  • How long a ladder can be carried lengthwise around a right-angled corner in a hallway?
  • A sphere has a cylindrical hole through its center 6 inches long. What is the sphere's remaining volume?
  • Connect the points in a 3 by 3 grid of points with 4 straight lines drawn without lifting your pencil from the paper.
  • Rearrange some blocks that make a 13x5 right triangle and they make the same triangle missing a single unit square. How so?
  • Two ladders of lengths A and B cross in an alley at a distance C above the ground. How wide is the alley?
• Matchstick puzzles:
  • A wine glass is made of 4 matchsticks. Invert it by moving 2 matches.
  • A 2x2 grid of squares is formed from 12 matches. Remove to matches to leave just 2 squares.
• Logic puzzles:
  • There are three light switches on a panel that control three lights you can't see from there. Which controls which light?
  • You have twelve gold coins and a balance. One coin is bad. Find it in three weighings.
  • Now you have N bags of coins and a scale; find the bad bag in one weighing.
  • A rotating square table has a glass at each corner. How can you turn all the glasses up or all down . . . ?
  • Four people want to cross a rickety bridge at night. The bridge can only support two people at a time. . . .
  • A farmer wants to cross a river with a wolf, a goat, and some cabbages, but the wolf will eat the goat and the goat will eat the cabbages if left alone together. . . .
  • Three missionaries and three cannibals want to cross a river with a boat that will only hold two people, but the cannibals will eat the missionaries if they outnumber them.
  • Five people and their dogs want to cross a river, using a boat that can hold any three of them. Each dog cannot be allowed to be with other people without their owner present. Lisa's dog can row the boat. . . .
  • N married couples are at a party. Each person at the party shakes hands with each other person he/she does not already know. . . .
  • Box A has a sign that says "The sign on box B is true and the gold is in box A." . . .
  • All but two of my flowers are roses; all but two are daisies; all but two are tulips. How many flowers do I have?
  • In any group of 6 people, must there be 3 mutual friends or three mutual strangers?
  • Three men named Smith, Jones, and Robinson work for a railroad. Smith plays billiards with the fireman. . . .
  • Five men live in consecutive houses, each house a different color, and each man has a different nationality, pet, favorite beverage, and brand of cigar. . . .
  • Several of these "paradoxes" are old chestnuts...
  • A man pays for a beer in Whozitland with a Whozitland dollar, and receives a Whatzitland dollar (worth 90 cents there) in change. . . .
  • Five friends eat at a restaurant of some foreign cuisine and order blindly. After three meals they have eaten any can identify all the items on the menu. . . .
  • 14 friends eat at a restaurant split into groups of 6 and 8. The next time they go they split into different groups of 6 and 8. How many times until everybody has eaten with everybody else?
  • A bundle of 15 wires runs through a long conduit in a large building. The wires are unmarked. Using only a continuity tester, how can you correctly label the ends of all the wires in the fewest trips?
  • 4 chess knights are at the corners of a 3x3 board; white at the left and black on the right. Swap them.
  • It's dark and I need to pull a matching pair of shoes/socks out of a drawer. How many do I need to ensure a pair?
  • ** Five pirates divide 100 gold coins by voting... **
• Geography puzzles:
  • Where does the new millennium begin first?
  • Which three U.S. states have three separate common boundary points?
  • Where can you drive south from the United States and enter Canada?
• Riddles, puzzles that depend on the interpretation of words or which have trick answers:
  • A man in the U.S. married ten women but broke no laws. How? (And other variations)
  • A ship at anchor has a ladder with nine rungs a foot apart showing above the water. After the tide rises five feet how many rungs show?
  • A man lies dead in the desert with an unopened pack on his back. How did he die?
  • There are six glasses of water, three full followed by three empty. Make them alternate by touching only one glass.
  • What has four legs in the morning, two legs in the afternoon, and three legs in the evening?
  • Why are manhole covers round? - some editor decided to delete this, with no /msg nor editor log entry. The answer was deleted around Feb. 12, 2001, the question around Feb. 14. I'm not putting it back up unless by popular demand.
  • A bookworm ate from the first page to the last page of a set of encyclopedias. How many pages did he eat?
  • A teaspoon from a gallon of water is mixed with a gallon of wine. Then a teaspoon of the mixture is transferred back to the water. Is there more wine in the water or water in the wine?
  • What is the product of (x-a)(x-b)(x-c) ... (x-z)?
  • **How can you measure the height of a tall building using a barometer? - apparently this one comes from Niels Bohr**
  • At 1/n hours before 12:00, I put 10 balls in a bin and take out 1. How many are left in the bin at 12:00?
• Other related nodes:
  • A nice, hard brain teaser
  • Brain Teasers, Brain Teasers: r2, Brain Teasers: r3

This expression comes from the nineteenth century play “The Broken Sword.” One of the characters is continually telling the same jokes. He does, however, alter them very, very slightly each time. At one point in the play he tells another character a joke involving a cork tree, the other character tells him it was a chestnut tree, he continues by saying that he has heard the joke twenty seven times and knows it’s a chestnut.