Riddle: There is a room. In this room,, there are two doors. One door leads to destruction, one to paradise. You have no way of knowing which is which. Also in this room are two robots. One robot always tells the truth, one always lies. There is no way to tell the robots apart. You are given a chance to ask either robot one question. What question can you ask either one that will tell you how to get to paradise?
Answer: You would ask either robot, "What door would the other robot tell me is paradise?"