How can a man go eight days without sleep?

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

10+10 and 11+11 can give you the same answer.

Explain how?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

By using all numbers, i.e. 123456789 and subtraction/addition, operators number 100 can be formed in many ways.
Example: 98 + 7 + 6 - 5 - 4 - 3 + 2 - 1 = 100

But if we add a condition use of the number 32 is a must. Then there are limited solutions.
One of such solution is: 9 - 8 + 76 + 54 - 32 + 1 = 100

Can you tell me any other solution?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

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?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

Replace the question mark with the correct number.

Find the missing number in the image below.