I am white when I am dirty, and black when I am clean. What am I?

Which is the smallest number that you can write using all the vowels exactly once?

What is full of holes but still holds water?

You are provided with a grid (as shown in the picture). Can you fill the squares with numbers 1-8 in a manner that none of the two consecutive numbers are placed next to each other in any direction (vertically, horizontally or diagonally?)

When 99 is considered higher than 100?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

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

why number 8549176320 is one of a kind?

A Man gave one of his sons 10 cents and another son was given 15 cents. What time is it?
Hint: Figure out the relation between time and number, is not so easy..:)

Can you make numbers like 24, using numbers 3,3,7 & 7 with any arithmetic operator?