What number when divided in half becomes zero?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

What has to be broken before you can use it?

I have a clock(12-hour format) and both the needles of the clock overlap at 12:00.
After how much time, they will overlap again?

The picture shows the dice results in each couple of throws. If they are actually following a pattern, can you find out the missing one?

Two friends were stuck in a cottage. They had nothing to do and thus they started playing cards. Suddenly the power went off and Friend 1 inverted the position of 15 cards in the normal deck of 52 cards and shuffled it. Now he asked Friend 2 to divide the cards into two piles (need not be equal) with equal number of cards facing up. The room was quite dark and Friend 2 could not see the cards. He thinks for a while and then divides the cards in two piles.

On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

What is the difference between a jeweller and a jailer?