I look at you, you look at me, I raise my right, you raise your left. What am I?

A man dies of old age on his 25 birthday. How is this possible?

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

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

Birbal was jester, counsellor, and fool to the great Moghul emperor, Akbar.
The villagers loved to talk of Birbal's wisdom and cleverness,
and the emperor loved to try to outsmart him.
One day Akbar (emperor) drew a line across the floor.
"Birbal," he ordered, "you must make this line shorter, but you cannot erase any bit of it."
Everyone present thought the emperor had finally outsmarted Birbal.
It was clearly an impossible task.
Yet within moments the emperor and everyone else present had to agree that Birbal had made the line shorter without erasing any of it.
How could this be?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

Find the next number in the series below.

6 18 270 72090 ?