The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

Find out the missing number in the picture attached:

What is harder to catch the faster you run?

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?

If in a car race, the man who came two places in front of the last man finished one ahead of the man who came fifth, how many contestants were there?

The more of this there is, the less you see. What is it?

John was piloting a plane behind a car but was never able to overtake it. Why?

What is the riddle which can be asked all day with a different correct answer each time.

Can you name an animal whose killing cannot be performed without spilling your own blood?