If eleven plus two equals one, what does nine plus five equal?

A woman lives in a Tall building thirty-six floors high and served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up than down. Why?

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

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?

How can you spell "White of an egg" in one word?
Hint: I know you can spell coke, poke, and joke.

What does an Island and the letter T have in common?

Count the number of lines in the image below ?

We know that the number 7 is the prime followed by a cube. Which next number is also a prime followed by a cube?

What is the fastest way to double your money?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?