Riddle: You buy a mansion. Right when you go inside, a robber jumps in through a window. He sees you and asks you to tell him which of the 3 switches in front of him turns on the attic light. If you lie to him, he will kill you. He lets you walk up the stairs once, but only once. Because you just bought the house, how will you know which switch turns on the attic light bulb?
Answer: You turn the 1st switch on and wait for 10 minutes. Then, you turn the 1st switch off and the 2nd switch on. You immediatly run up to the attic. If the light is on, the 2nd switch is the one that turns the light on. If the light is off, you feel the bulb. If the bulb is hot, it's the 1st switch. If the bulb is not hot, it's the 3rd switch.