It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Why do people go to bed?

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?

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?

Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

I travel all around the world but always stay in the corner. What am I?

What happened when the wheel was invented?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

What numbers should go on the bottom line?
3 6 9 15
8 2 10 12
11 8 19 27
19 10 29 39
? ? ? ?

What does below rebus means ?