Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.

Filtered by tag: mathematics

15 10 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
2.2
13 6 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
6.0
9 4 Carpeting a Donut
Given two concentric circles and a chord of the outer circle, tangent to the inner circle, of length 25m, find the area between the two circles. See illustration. No other information needed, all you n ...
Doable
5.7
8 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
3.8
8 6 The double-square number problem
It's said that a number N with 4 digits is a double-square number when it equals the sum of the squares of two numbers: one formed by the first two digits of N, in the order they appear in N and the ot ...
Math mathematics Submitted by Guilherme
Hard
8.2
8 Unfair Coin
Say you have an unfair coin: a coin whose probability of flipping heads and flipping tails is unknown but nonzero. Can you design a game where you and your opponent have an equal chance of winning?
Doable
5.3
5 6 Partitioning a set
In how many ways can a set of r objects be partitioned into subsets of k objects such that: all subsets are mutually exclusive each of k-object subset appears in exactly one of the partitions [Partit ...
Hard
8.7
4 5 Binary 5 digits
What is the base 10 equivalent of the highest 5 digit binary number?
Easy
2.0
4 1 Clock Hands - Google Interview Question
How many degrees are there in the angle between the hour and minute hands of a clock when the time is a quarter past three?
logic mathematics Submitted by Valentin
Doable
3.6
4 Don't Hang Yourself
A fool wants to tie a rope around the earth. So he buys a rope of 40,000 KM and ties it around the world. His neighbour, also a fool, wants to do the same only he wants the rope on sticks 1 meter abo ...
Easy
2.8
3 Divide 1 to 20
What is the smallest whole number that can be divided by any number from 1 to 20 (inclusive) and not leave a remainder? For example, 60 is the smallest number that can be divided evenly by all the n ...
mathematics Submitted by Aakash
Doable
5.0
3 Gone Camping
Camp Crona’s cook, Allison, was just about to begin preparing the picnic lunch for all the campers. She already knew she needed to fill 55 bowls of the same size and capacity with the same amount of fo ...
mathematics Submitted by Aakash
Easy
3.0
2 2 Nice to meet you
At a secret meeting, everyone shakes hands exactly once with every other person present. Altogether there are forty-five handshakes. How many people attended the meeting?
Easy
2.8