Which number should replace the question mark?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

Can you count the number of triangles in the given picture?

What Deficiency does the below rebus represent?

VIT_MIN

A woman lives in a skyscraper thirty-six floors high and is 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?

What happened when the wheel was invented?

You can take four of the five letters out of this word, but the pronunciation never changes. What is the word?

What can go through glass without breaking it?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

What does this rebus means ?