Can you convert the number zero(0) into a positive number using just one mathematical operator ?

You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.
There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.
You can, however, ask one robot one question. The problem is one robot always tells the truth, the other always lies and you don't know which is which.
What is the question you ask?

How many bananas can you eat if your stomach is empty?

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

In a jungle where there are no street lights or any other artificial source of lights, I notice a black snake crossing the road.
How did I get sight of the snake?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

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

There was a blind man. He had four socks in his drawer either black or white. He opened it and took out two socks. Now the probability that it was a pair of white socks is 1/2.

Can you find out the probability that he had taken out a pair of black socks ?

That attorney is my brother, testified the accountant.

But the attorney testified he didn't have a brother.

Who is lying?

How could a baby fall out of a twenty-story building onto the ground and live?