A room contains three light switches connected to three turned-off bulbs in another room. You can flip switches in the first room as much as you like, but you can make only one trip into the room with the bulbs. One of the switches is broken and does nothing. You turn Switch A on for 10 minutes, then turn it off and turn Switch B on. Walking into the bulb room, you find Bulb 1 is hot and off, Bulb 2 is lit, and Bulb 3 is cold and off. Which switch is broken?
Switch C
Bulb 1 was controlled by Switch A (hot from being on for 10 minutes). Bulb 2 is controlled by Switch B (currently on). Bulb 3 remained cold and off despite Switch C being untouched, showing Switch C is the broken switch that controls nothing.
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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