Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.
3 4 Products Algorithm
Given an array A[1...N] of integers, create an array O[1...N] where O[i] = the product of all elements in A except for the ith element. For example, if N = 3, and A = {6, 4, 2}, O = {8, 12, 24} The t ...
Doable
4.0
4 7 Balloon Business
You’re sitting in a stationary car. There’s a helium balloon tied to its floor. You accelerate and, obviously feel like you’re being pushed backwards (against the direction of your acceleration). W ...
physics science logic Submitted by Valentin
Doable
4.0
8 2 All Apples
On the market, mrs. Jones and mrs. Smith sell apples. Mrs. Jones sells her apples per two for 0.50 euro. The apples of Mrs. Smith are a bit smaller; she sells hers per three for 0.50 euro. At a certa ...
mathematics ratios Submitted by Valentin
Doable
4.0
18 4 3 Men and a Hotel Room
Three men decided to split the cost of a hotel room. The hotel manager gave them a price of $30. The men split the bill evenly, each paying $10, and retired to their room. However, the manager real ...
Submitted by Valentin
Doable
4.2
6 6 The Female Star
My first two letters are a man. The first three a woman. The first four are a brave man. And in whole I am a brave woman.
riddle word puzzle Submitted by Valentin
Doable
4.3
7 5 Burning Rope
There are two lengths of rope. Each one can burn in exactly one hour. They are not necessarily of the same length or width as each other. They also are not of uniform width (may be wider in middle th ...
Submitted by Ravi
Doable
4.3
4 2 The Classic Weights & Scale
You have 8 lead marbles, one of which is heavier than the rest. What is the minimum amount of “weightings” (i.e. with a see-saw scale) you need to do to guarantee finding the odd one out?
Submitted by Valentin
Doable
4.3
3 1 What number is next?
What number comes next in this sequence? 4, 20, 56, 120, 220, ?
Submitted by Aakash
Doable
4.3
5 1 3 Brilliant People
There are three genii standing in a row in a room facing the same direction. Thus, the genius at one end can see the two genii ahead of him, the genius in the middle can only see the one genius ahea ...
Submitted by Ravi
Doable
4.3
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
6 7 Death by drawing?
You are a prisoner in a strange foreign land, and a random drawing will decide your fate. You are given 2 bags, 10 white marbles, and 10 black marbles. You are to place the marbles in the bags in any a ...
probability Submitted by Gene
Doable
4.4
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
4 4 Time To Fuse
You have a string-like fuse that burns in exactly one minute. The fuse is inhomogeneous, and it may burn slowly at first, then quickly, then slowly, and so on. You have a match, and no watch. How do ...
physics logic rates Submitted by Valentin
Doable
4.5
10 4 Two Trains
Two trains (Train A and B) with 200 km between them are travelling towards each other at 100km/h. A mosquito, initially standing on the front of Train A, starts travelling towards Train B at 150km/h. O ...
Math physics rates Submitted by Ravi
Doable
4.5
4 5 Attic Light Switch
A downstairs panel contains three on-off switches. One of them controls the lamp in your attic. Using only ONE trip up to the attic, how do you determine which switch controls the lamp?
Doable
4.7