The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

You knock a Table over in the library, and suddenly 20 eyes are looking at you.

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

I have teeth but i don't bite. Who Am I ?

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?

A man hijacks an aeroplane transporting both passengers(8 of them) and valuable cargo. After taking the cargo, the man demands nine parachutes, puts one of them on, and jumps, leaving the other eight behind. Why did he want eight?

When it is alive we sing, when it is dead we clap our hands. What is it?

A newspaper is supposed to have 60 pages, but pages 24 and 41 are missing.
Which other pages won't be there?

What is the centre of gravity?

Most people think of me as money. But when they find me in the water, they won’t get any money out of me. What am I?