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

Name a key which is hardest to turn.

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Do you know of a place where the wind blows south and then suddenly shifts direction towards the north?

There was a competition where the contestants had to hold something. At the end of the event, the winner was a person who had no hands or feet. What was it that the contestants had to hold?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

What runs around the whole yard without moving?

A woman lives in a skyscraper thirty-six floors high and is served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up than down. Why?

Can you divide the below-given shape into four equal and identical pieces?