Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.
12 13 Bit Pair Swap
In one line of C or Java, how would you swap every pair of bits in a byte? That is, swap bits 0 and 1, 2 and 3, 4 and 5, 6 and 7. Example: 0110 1010 becomes 1001 0101.
Doable
6.3
3 2 Brain Teaser 56
Answer Yes or No to this brain teaser
Easy
2.5
2 6 How many?
As I was going to St. Ives, I met a man with seven wives. Each wife had seven sacks. Each sack has seven cats. Each cat had seven kits. Kits, cats, sacks, and wives, How many were going to St. Ives? ...
Submitted by Gene
Easy
3.0
3 6 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
6.0
7 8 Survivor
There are 1500 people sitting around a circular table. They are numbered in a regular manner (1 to 1500 along the table). Now, the 1st person gets a sword and kills the 2nd person. He then gives the s ...
Submitted by Shaheen
Hard
8.4
11 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
8.1
10 16 3 Coins
Not sure what the answer is, ideas welcome! You have 3 coins, one always comes up heads, the second always comes up tails, and the third is a fair coin. You select a coin at random. After selecting ...
Math help Submitted by city_slick
Easy
3.0
6 6 Binary 5 digits
What is the base 10 equivalent of the highest 5 digit binary number?
Easy
2.0
11 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
14 1 100 Light Bulbs
There are 100 light switches, all of them are off. First, you walk by them, turning all of them on. Next, you walk by them turning every other one off. Then, you walk by them changing every third on ...
mathematical logical Submitted by Aakash
Hard
7.7
14 7 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
17 2 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
4.7
9 9 The Monty Hall Problem
You’re on a game show, and you’re given the choice of three doors: Behind one door is a car and behind the other two doors are goats. You pick a door, say No. 1, and the host, who knows what’s behind ...
Doable
5.5
9 6 Sum of Two Prime Numbers
If p, q > 2 are consecutive in set of primes. Since p,q can only be odd number, (p+q) is an even number. Can (p+q)/2 be prime? from http://republicofmath.com/
Submitted by MoralMachine
Easy
3.2
9 7 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
6.4