You are standing outside a closed door. On the other side of the door is a room that has three light bulbs in it. The room is completely sealed off from the outside. It has no windows and nothing can get in or out except through the door. On the outside of the room there are three light switches that control each of the respective light bulbs on the other side of the door. Your assignment is to determine which light switch controls which light bulb. You are allowed to enter the room only once, and once you come out, you must be able to state with 100 percent certainty which light switch controls which light bulb. Lisa bragged that she solved this brainteaser when The Simpsons first aired in 1989 and she thinks you can, too.

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Answer: Turn on switch one for 15 minutes and then turn it off. Then turn on switch two and enter the room. The lit bulb clearly belongs to switch two, yet there are two dark bulbs. Touch them both. The warm bulb belongs to switch one and the cold bulb to switch three. Wait, what about LEDs? Ah, that's why I mentioned Lisa first solved the puzzle in 1989. Now if time was not an issue, perhaps you could flip one switch on and off for years until (hopefully) it burned out. Leave that switch on, turn on another, and enter the room. Two bulbs should be dark. Unscrew the two dark bulbs and to determine which one is burnt out, a) shake ‘em or b) look for a dark spot. Perhaps you could even stick your finger into the socket and see which one shocks you (revealing the socket that held the burned out bulb since you turned it back on), but that’s not recommended.