There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?

Move four matchsticks to the below square to form three squares?

Identify Me

Hint1: I am a god
Hint 2: I am a planet
Hint 3: measurer of heat

What does this rebus puzzle means ?

I shave every day, but my beard stays the same. What am I?

Count the number of triangles in the given picture.

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

10+10 and 11+11 can give you the same answer.

Explain how?