What is black when you buy it, red when you use it, and gray when you throw it away?

Two old friends, Jack and Bill, meet after a long time.

Three kids
Jack: Hey, how are you, man?
Bill: Not bad, got married and I have three kids now.
Jack: That's awesome. How old are they?
Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.
Jack: Cool..But I still don't know.
Bill: My eldest kid just started taking piano lessons.
Jack: Oh, now I get it.

How old are Bill's kids?

A man is found unconscious in front of a store at two in the morning. His head is bleeding and there’s a brick laying next to him. When the police arrive, they carry the man to jail. Why did they arrest him?

Can you move 2 matchsticks to form four equal sized squares.

What came first, the chicken or the egg?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

What is the last thing you take off before bed?

What four weights can be used to balance from 1 to 30 pounds?

You have an empty wine bottle with a cork that has been secured at the top in a normal way. There is a metal ring inside the bottle that is suspended by a string.

How can you make the metal ring drop to the bottom if you are not allowed to touch anything - not the bottle, not the cork, not the thread and not the ring?

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