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Light bulb (Posted on 2002-05-16) Difficulty: 2 of 5
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.

You are allowed to enter the room only once (the bulb is not visible from outside). How can you determine which of the three switches turns on the light bulb?

See The Solution Submitted by Half-Mad    
Rating: 3.2500 (24 votes)

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Solution my way | Comment 10 of 17 |
You first flip on one switch and then wait for about 10 to 15 minutes.  Then you flip off that switch and flipo on another one.  Then you go into the room.  If the bulb is lit, then the switch you just flipped turns on the light bulb.  If the bulb is not lit, but is hot, then the first switch turned on the bulb.  Finally, if the bulb is neither lit nor hot, then the switch you did not handle turns on the lightbulb.
  Posted by logischer Verstand on 2004-04-13 17:18:23
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