Why Aeroplane windows are round?
I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?
Use the numbers 2, 3, 4 and 5 and the symbols + and = to make a true equation. Conditions: Each must be used exactly once and no other numbers or symbols can be used.
A network of 20 x 10 squares is given to you. Can you calculate how many unique squares and rectangles can be formed combining two or more individual squares ?
Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?
Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?
Which tank will fill first?
Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.
I had an infinite supply of water and 5 litres and 3 litres jars. How would you measure exactly 4 litres in the least number of steps?
Count the number of triangles in the given picture.
How many triangles can you count in the figure given?
There is a cryptic organization called Cicada 3301 that posts challenging puzzles online, possibly to recruit codebreakers and linguists.
