What does this Rebus Picture means ?

Which number should replace the question mark?

What is the word or phrase?

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?

When is the top of a mountain similar to a savings account?

What does this rebus riddle means ?

Why is it against the law for a man living in Delhi to be buried in Mumbai?

A man was just doing his job when his suit was torn. Why did he die three minutes later?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Solve the mathematical equation in the picture below.