Question

A man is on a game show. he is presented with two doors, one on the left, and one on the right. behind one is 2 million dollars, and behind the other is a donkey. choose the correct door to win the prize. there are also two men in front of the doors, and they know which door leads to the millions. one wears a black hat, the other wears a white hat. the host explains that one of the men is a liar, and will always lie, and the other man will always tell the truth - but you don't know which is which. you can only ask one of the men only one question. what is the question, and which man do you ask to ensure you win the money?

Answer 1

Ask either of the men who are in front of the doors: "If you were the other man, which door would you tell me leads to the 2 million dollars?" 

The truth-teller, positioning himself as a liar, will say the door which does not have the 2 million dollars.
The liar, positioning himself as a truth-teller, will also say the door which does not have the 2 million dollars because he is a liar.