Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.
2 479 The Bookworm
Looking onto a shelf you see three books each labeled Volume 1, Volume 2, and Volume 3 respectively. Each book is 2.5 inches thick; that is the pages are 2 inches, and each cover .25 inches. A bo ...
Submitted by Aakash
Doable
5.2
8 225 Non-Adaptive 12 Identical Balls
Okay - so I posted this puzzle to reddit a few weeks ago and one guy had the following comment: Same problem, but your solution must be non-adaptive. IOW, specify the weighings that you will make up f ...
Math logic unsolved Submitted by Aakash
Hard
9.0
10 211 Fork in the road
You are walking down a road and arrive at a fork that splits the road into two separate paths. When you reach, you meet two identical twins, each standing at the edge of one of the two paths. You h ...
Submitted by Aakash
Doable
6.0
46 36 Charlie and the Chocolate Factory
Charlie once visited chocolate factory to buy some chocolates.Chocolate cost Rs. 3 each and he had only Rs. 45.He was disappointed. He wanted more. But when he reached the factory he was amazed. There ...
Easy
2.4
54 41 All the King's Wine
So there's this king. Someone breaks into his wine cellar where he stores 1000 bottles of wine. This person proceeds to poison one of the 1000 bottles, but gets away too quickly for the king's guard ...
logic mathematical Submitted by Aakash
Hard
7.6
14 80 Coin Flip
On Monday, you flip a coin all day. You start flipping it until you see the pattern Head, Tail, Head. You record the number of flips required to reach this pattern, and start flipping again (and co ...
Math statistics Submitted by Aakash
Doable
6.0
45 12 The Sinking Island
You and 3 friends are on an island that is sinking. There is one bridge from the island to the mainland that supports at most 2 people at once. However, it's dark outside so anyone crossing the bridge ...
Doable
4.3
37 27 No if() Only abs()
Given two variable a and b, construct a function f(a,b) which return the maximum one in {a,b}. You can only use +- · / and abs() (to take the absolute value). NO if() is allowed in your construction. ...
Submitted by MoralMachine
Doable
5.8
27 45 12 Identical Balls
You have 12 identical balls. One of them is slightly different in weight than the rest. You have three weighs of a balance scale to determine which ball is different and whether it is heavier or li ...
logic brain teaser Submitted by Valentin
Doable
6.2
17 31 Multiples of 8 plus 1
Squaring the first several odd numbers reveals the following pattern: 3 squared = 8 + 1 5 squared = 24 + 1 7 squared = 48 + 1 8, 24, and 48 are all multiples of 8. Does this pattern hold for all squa ...
Doable
4.5
11 25 Gold or silver?
What weighs more, a pound of silver or a pound of gold?
riddle chemistry Submitted by Jango
Easy
2.0
18 13 Cocktail Party
You are observing a cocktail party that has seven guests. You notice that each guest shakes hands with one another once they meet, but never again. How many handshakes occurred during the cocktail part ...
Easy
2.4
13 23 Black and White Hats
There are 100 prisoners in jail. Their guards decide to play a game with them. Here's what happens: 1) The prisoners are lined up in a single file, front to back, such that the prisoner at the back of ...
logic prisoners hats Submitted by Aakash
Hard
8.5
19 11 Going to the Track
The London racetrack needs to submit its top three horses to the Kentucky Derby next month in order to compete for a prize. However in a recent electrical storm, all the racetrack's previous race histo ...
logic mathematics Submitted by Nikhil
Doable
6.2
15 14 Swap Variables in Place without XOR
Suppose you have two variables, a and b. How can you swap their values without using a temporary variable and also without using the bitwise operator XOR?
Doable
3.9