Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

In the attached figure, you can see a chessboard and two rooks placed on the chess board. What you have to find is the number of squares that do not contain the rooks. How many are there?

In a university, a professor gave a set of three problems to the three brilliant students of his class. See the image for the questions.

It is always ahead of me yet I can never see it. What is it?

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

This is a classy optical illusion puzzle. What more you can find except bricks in the image below?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

Take number 1000 and then add 20 to it.
Now add 1000 one more time.
Now add 30.
Now add 1000 one more time.
Now add 40.
Now add 1000 one more time.
Now add 10.

What is the total?

Which tank will fill first?