You find yourself in a room with two doors. One door leads to freedom and the other to deadly traps. Two guards stand there: one always tells the truth and one always lies. You may ask one guard a single question to pick the safe door. What do you ask?
Ask either guard: "If I asked the other guard which door leads to freedom, what would he say?" Whichever door is indicated, choose the opposite one—that door leads to freedom.
