What is more useful when it is broken?

Can you count the number of quadrilaterals in the picture below?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

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?

What Time Should the last watch show in the below figure?

You need to remove two matchsticks to make the below equation true. Can you do it ?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

I have a mouth but I don't eat.
I have a bank but have no money.
I have a bed but i dont sleep.
I wave but have no hands.

Who Am I ?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

In the picture, you can see a chess board. On the top left position, the K marks a knight. Now, can you move the knight in a manner that after 63 moves, the knight has been placed at all the squares exactly once excluding the starting square?