What goes up but never comes down?

What number when divided in half becomes zero?

How can you make number one disappear by adding something to it?

How many letters are in the alphabet?

What word is pronounced the same if you take away four of its five letters?

Which tank will fill first?

What kind of band never plays music?

There are two guys standing face to face in a room. On a wall, there is a clock. One of those is a prophet. He tells the other guy that he will be stabbed in the back in five minutes.

Shocked to hear that, the other guy stares at the clock. Just after the five minutes, he is stabbed on the back. Can you tell what happened?

Replace the question mark with the correct number below.

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?