I have teeth but i don't bite. Who Am I ?

A man is trapped in a room. The room has only two possible exits doors. Through the first door there is a room constructed from magnifying glass. The blazing hot sun instantly fries anything or anyone that enters. Through the second door there is a fire-breathing dragon. How does the man escape?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

You can see it everyday, But cannot touch it at will. What is it?

If you’ve got me, you want to share me; if you share me, you haven’t kept me. What am I?

Three friends decide to distribute the soda cans they had among them. When all of them had drunk four cans each, the total number of cans that remained was equal to the cans each one of them had after they had divided the cans.

Can you calculate the total number of cans before distribution?

I always drive my customer away.

Who am I?

Can you count the number of blocks in the picture below?