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:
Date/time puzzles:
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:
Matchstick puzzles:
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:
Riddles, puzzles that depend on the interpretation of words or which have trick answers:
Other related nodes: