Welcome to MindCipher, a social repository of the world's greatest brain teasers, logic puzzles and mental challenges.
7 7 Interview Question - Databases
This is a common interview question at companies like Google and Amazon: “Explain a database in three sentences to your eight-year-old nephew.” This question has an infinite number of solutions. Fee ...
5 8 Find the Missing Number
In this table, each row across follows the same pattern of numbers. See if you can discern the pattern and fill in the missing number in the bottom row. 7 4 8 3 9 7 6 5 10 ? ...
patterns Submitted by Ravi
7 3 Tea and Wine
You take a spoon of wine from a barrel of wine and put it into your cup of tea. Then you return a spoon of the (non-uniform) mixture of tea and wine from your cup and put it in the barrel. Now you ha ...
Math logic Submitted by Ravi
6 8 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
2 4 What is the sum of 1+2+3+4+5 . . . (forever)?
What is the sum of 1 + 2 + 3 + 4 . . . all the way to infinity?
infinity Submitted by Tarun245
5 6 Balloon in an Elevator
A person is holding on to a helium balloon in an elevator. The elevator cable snaps, and at the exact same moment, the person lets go of the helium balloon. In the perspective of the person in the el ...
physics relativity Submitted by Aakash
5 5 Betsy and Patsy
“We were born on the same day of the same year,” said Betsy. “And we have the same mother and father,” said Patsy. “But we’re not twins!” the two exclaimed. Can you explain?
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
9 1 Three Idols
Here's a classic: Three gods A, B, and C are called, in some order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a comp ...
3 1 There are only 4 circles and none of them touch
Source: reddit.
optical illusion Submitted by Ravi
5 2 Matchsticks
This is a classic Martin Gardner puzzle. See the picture - the four matchsticks represent a martini glass and the match head represents an olive. Move just two matches so that the glass is reformed bu ...
logic spatial Submitted by Aakash
9 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?
3 8 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
3 5 Cooking Time
A cook must put a souffle exactly 9 minutes at the oven, but he only have a 7 minutes hourglass and a 4 minutes hourglass. How can he measure 9 minutes with those clocks?
logic Submitted by Ravi
9 1 Mutilated Chessboard Problem
Suppose a standard 8×8 chessboard has two diagonally opposite corners removed, leaving 62 squares. Is it possible to place 31 dominoes of size 2×1 so as to cover all of these squares?
geometry chess proofs Submitted by Ravi