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?

The first person saw the bridge step on it and crossed,
the second person saw the bridge did not step on it but crossed,
the third person did not see the bridge did not step on it but crossed.
Who are these people?

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

Can you identify the Oscar-winning movie from the rebus below?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

The day after tomorrow will be three days before Tuesday. Can you find out what is today?

Decode below rebus
D
N
A
T
S , D

The dirtier I get, the whiter I look. Who am I?

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