There are three light switches outside a closed, unlit room corresponding to three incandescent lightbulbs inside. All switches are currently OFF. You may turn the switches ON or OFF as much as you like, but you can only open the door and enter the room ONCE. How can you determine which switch controls which bulb?
Turn Switch 1 ON for 10 minutes, then turn it OFF. Turn Switch 2 ON, and immediately enter the room.
The bulb that is lit corresponds to Switch 2. The bulb that is unlit but warm to the touch corresponds to Switch 1. The bulb that is unlit and cold corresponds to Switch 3.
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: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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