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This question already has an answer here:

There is a room with a single light bulb in it. Outside the room there are three light switches. You cannot see inside the room at all. Only one light switch turns on the light bulb. You may only enter the room once to find out which switch turns it on. The goal is to figure out which light switch turns on the light.

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marked as duplicate by A E, Joe, warspyking, pacoverflow, Len Dec 5 '14 at 23:13

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ This is a dupe - I don't have time to find it right now. Just a heads-up. Sorry :-) $\endgroup$ – Joe Dec 5 '14 at 20:38
  • $\begingroup$ Yea but isnt that with 4 switches? i did metion it maybe a duplicate but slightly different. i wont be offended if it gets marked as such. i just thought to share the version i learned $\endgroup$ – theeppright Dec 5 '14 at 20:42
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    $\begingroup$ That's one's three switches too I'm afraid. No worries, this one'll get closed as a duplicate but don't take it to heart, you're very welcome to join us here on puzzling.SE nonetheless! :) $\endgroup$ – A E Dec 5 '14 at 20:45
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    $\begingroup$ :) thx for being so kind! other people can be pretty nasty about this type of thing thanks again. $\endgroup$ – theeppright Dec 5 '14 at 20:46
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    $\begingroup$ no worries @theeppright! ;) $\endgroup$ – A E Dec 5 '14 at 21:20
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Label the switches A B and C.

Turn on A and B and wait for a while, then turn off A. Enter the room.

How to determine the switch?

On -> B
Off and cold -> C
Off and hot -> A

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  • $\begingroup$ good job! not like it was too hard :/ thx for answering! $\endgroup$ – theeppright Dec 5 '14 at 21:40
  • $\begingroup$ @theeplright No problem. It may not be hard for people here but it can be a good puzzle for people in real life :P $\endgroup$ – warspyking Dec 5 '14 at 21:44

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