What occurs twice in a week, once in a year but never in a day?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

Assume the given figure to be a delicious doughnut. Yes, now you can concentrate more on the puzzle. So you have this delicious doughnut in your refrigerator when your friends come knocking at the door. There are eight of them. Now you have to make three cuts in this doughnut so that each one of you nine people can enjoy a piece of it. Neither you nor your friends would mind the size of their piece as long as they are getting it. How will you do it?

I add 5 to 9 and get 2. The answer is correct, so what am I?

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

French Police inspects a room where there are no windows, no doors, no tables and is almost empty expect there is just a puddle of water. They found a dead man who obviously hung herself from the ceiling, but they are not able to figure out how this had happened.

John and Jacob entered the crime scene and easily able to solve the case.

How did the man die?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

How can you drop a raw egg from a height onto a concrete floor without cracking it?

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

Explain how?