You're trapped in a room with two doors. one leads to certain death 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 a question. the problem is one robot always tells the truth, the other always lies and you don't know which is which. what's your question?

     You ask one guard what the other guard would say is the door that will lead you to freedom. Then, you go through the other door. Let's call the freedom door door 'A' and the other door 'B'. If you ask the truthful guard if the other will say door A is the freedom door, he would say the other guard would say no. you go through door A and you're free. You ask the liar guard if the other would say door B is the freedom door. He would say that the truthful guard would say yes (because he is a liar) and you would go through the other to freedom.