How many times do a clock's hands overlap in a day ?

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?

Can you find the key in the picture below?

A man hijacks an aeroplane transporting both passengers(8 of them) and valuable cargo. After taking the cargo, the man demands nine parachutes, puts one of them on, and jumps, leaving the other eight behind. Why did he want eight?

What is the next number in this series?

4,12,84,3612....

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

John needs to purchase 100 chocolates from three different shops and he has exactly 100 rupees to do that which he must spend entirely. He must buy at least 1 Chocolate from each shop.

The first shop is selling each chocolate at 5 paise, the second is selling at 1 rupee and the third is selling at 5 rupees.

How many chocolates should he buy from each shop?

What does it mean?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?