Can you replace the question mark with the correct number?

On a certain day, John celebrated his birthday. Two days later, his older twin brother Jacob celebrated his birthday.

Is this even possible? How can it be?

One absent-minded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he travelled on foot to his friend's place a few miles down the straight desert road. He stayed at his friend's house for the night and when he came back home, he knew how to set his clock. How did he know?

Three ants are going up a hill, one behind the other. The last ant then says to the other ants, 'There is an ant behind me!'' How come?

The more you take me, the more you leave me behind.
Who Am I?

When I asked a girl's name she told me her name is the date '07/09/2001'.

I thought for a few seconds and then I got her name. Do you?

What is wrong in the below Picture?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

I am the fastest animal but cannot climb the tree. What am I?

What goes through cities and fields, but never moves?