A light bulb inside a closed room is controlled by three switches outside the room labeled 1, 2, and 3. You start outside with all switches off. You can flip the switches however you like, but you may enter the room only once. How can you determine with certainty which switch controls the light bulb?
Turn on Switch 1 for 10 minutes, turn it off, turn on Switch 2, then enter the room.
If the light bulb is on, Switch 2 controls it. If the bulb is off but warm to the touch, Switch 1 controls it. If the bulb is off and cold, Switch 3 controls it.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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