If 21x = 79x, what is the value of x?

Replace the question mark with the correct number in below Picture:

Remove two matchsticks to make the below equation correct.

A father's child, a mother's child, yet no one's son.

Who am I?

Find The Missing Number In the Sequence.
6 25 64 ? 32 1

I have two coins.
* One of the coins is a faulty coin having a tail on both sides of it.
* The other coin is a perfect coin (heads on side and tail on other).

I blindfold myself and pick a coin and put the coin on the table. The face of the coin towards the sky is the tail.

What is the probability that another side is also tail?

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

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?

From a pack of 52 cards, I placed 4 cards on the table.

I will give you 4 clues about the cards:

Clue 1: Card on left cannot be greater than the card on the right.
Clue 2: Difference between the 1st card and 3rd card is 8.
Clue 3: There is no card of an ace.
Clue 4: There are no face cards (queen, king, jacks).
Clue 5: Difference between the 2nd card and 4th card is 7.

Identify four cards?

Why do you find that most of the buildings are deprived of the 13th floor?