using four eights (8) and a one (1) and one mathematical symbol , create the number 100

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

How many triangles can you find in this given picture?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

Can you discover the missing number in this series?

37, 10, 82
29, 11, 47
96, 15, 87
42, ?, 15

A professor thinks of two consecutive numbers between 1 and 10.
'A' knows the 1st number and 'B' knows the second number

A: I do not know your number.
B: Nor do I know your number.
A: Now I know.

What are the four solutions for this?

If one and a half boys, eat one and a half burgers in one and a half hours.

How many burgers can 9 boys eat in 3 hours?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10