Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.
0 4 Plane In The Wind
An airplane flies in a straight line from airport A to airport B and back. It has constant engine speed and no wind. Will its total flight time increase, decrease or stay the same if throughout bot ...
Submitted by Valentin
Doable
4.0
0 4 Cutting Numbers
When is Seven half of Twelve?
lateral thinking Submitted by Ravi
Easy
3.0
5 A Pharmacist's Nightmare
You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated p ...
Submitted by Ravi
Hard
7.0
3 4 Power of 2 (Microsoft Interview)
Given any number n, using one line of C (using no external libraries or functions) code, determine if n is a power of 2. Return 1 if n is a power of 2 and 0 if not.
bitwise powers Submitted by Aakash
Doable
6.0
3 1 What number is next?
What number comes next in this sequence? 4, 20, 56, 120, 220, ?
Submitted by Aakash
Doable
4.3
2 6 The Easy Sum of 1..100?
Quick,without using a calculator, what is the sum of all numbers between 1 and 100 inclusive? Or 1..10 for that matter..
Submitted by Valentin
Easy
2.5
4 4 Left Hands Only
Assume there are approximately 6,000,000,000 (6 billion) people on Earth. What would you estimate to be the result if you multiply together the number of fingers on every person’s left-hands? For t ...
Submitted by Aakash
Hard
6.8
6 3 Clever Commuter
Every day, Fred takes the train to travel from his work back to Alkmaar, his place of residence. Usually, he arrives at the station of Alkmaar at six o’clock, and exactly at that moment he is picked ...
Submitted by Valentin
Hard
7.5
5 11 The Stealing Mailman
This is a fairly simple problem that can cause some people trouble. Kevin and Sophia want to mail high confidential letters between each other. They know that the mailman is crooked and opens the le ...
logic cryptography Submitted by Ravi
Doable
6.5
1 3 Stuck in a brick building
A man is stuck inside an all brick building (floor, ceiling, and walls are all brick), that has no windows and no doors, and inside with him he has only a wooden board and a saw, how does he get out? ...
Submitted by Valentin
Doable
5.3
4 6 Guilty Innocence
I am a drug dealer. I have been questioned by the police with all of my drugs surrounding me, but I was not arrested. Why?
Easy
2.8
2 13 Good luck at an interview with Google
I just came across these Google interview questions… impossible: How many golf balls can fit in a school bus? How much should you charge to wash all the windows in Seattle? How many piano tuners are ...
google open-ended Submitted by Valentin
Hard
7.0
7 7 The Neighbourhood
People say Einstein suggested that 98% of the world’s population couldn’t figure out the answer to this puzzle. It is not for the faint of heart: There are 5 houses each with a different color. Th ...
Hard
7.5
4 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
4 10 Don't Mate in One
This problem was first publicized by Karl Fabel, a German chess problemist. Find a move for white that will not result in an immediate checkmate of the black king.
logic chess Submitted by Aakash
Doable
6.6