#9

You are in a room with three light switches. Each light switch turns on one light in the next room. The first light switch does not necessarily go to the first light bulb. The bulb and switch can match up in any order. You can only go to the room with the lightbulbs once. In that one time you must determine which light switch goes to which lightbulb. The room is not transparent you cannot peak under the door and there are no holes in the walls and no windows. How do you tell which light switch goes to which light bulb?

Answer:

You turn on the first switch for five minutes then turn it off. Then, turn on the second switch and go to the light bulb room. The bulb that is on is the second switch, the bulb that is off but hot is the first switch and the bulb that is off and cold is the third switch.