Who can jump higher than a Mountain?

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

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

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

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

What two things can you never eat for breakfast?

For an extra income, John decided to work at a Hotel for one hour daily. The manager offers him that they will pay him $11 after every 11 days.
However, John offered a different proposition to the manager. The offers stand as:
He will be paid just a penny on his first day.
Two pence will be paid on the second day,
Four pence will be paid on the third day.
And so on till the 11th day.

Should the Hotel manager accept his offer?

Find the missing number in the image below.

Prove that twice of ten is the same as twice of eleven.

Spot what is wrong here in below Picture?