Bulb switches riddle

A light bulb is hanging in a room. Outside of the room, there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are ‘off’ and the bulb is not lit.

If it is allowed to check in the room only once to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on?

SherlockHolmes Expert Asked on 14th September 2018 in Interview Puzzles.
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  • 1 Answer(s)
    Best answer

    Switch on the first button for a few minutes, then switch it off. Then switch on the second button and enter the room, if the bulb is not lit and if the bulb is hot then the first button is the right one, if the bulb is neither lit nor hot then the third button is the right one and if the bulb is lit then obviously the second bulb is the right one.

    Amannegi4 Curious Answered on 14th September 2018.
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