Three switches |  |
You're standing in front of a room with one lightbulb inside of it. You cannot see if it is on or off. Outside the room, there are 3 switches in the off positions. You may turn the switches any way you want to. You stop turning the switches, enter the room and know which switch controls the lightbulb.
How?
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Turn 2 switches "on" and leave 1 switch "off" and wait for about a minute. Then enter the room, but just before you enter, turn one switch from "on" to "off". Once in the room, feel the lightbulb - if it is warm, but off, it has to be the last switch you turned off. If it is on, it has to be the switch left on. If it is cold and is off, it has to be the switch you left in the off position.
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Comments
I would just punch a hole in the wall and look through it.- Josh (4 May 2010)
Why dont u see trough the window it did not specify if the room has windows
- why (29 Jun 2010)
uhhmm ... a bulb that is not lit , will not generate heat. So how can that be? and switching it all on wouldn't hurt anyone , and the statement didn't say if one switch should only be on
- BLUEheart (3 Jul 2010)
brilliant!
- (6 Apr 2011)
Technically, yo don't know if the light is on or off to start with. And so even the switches are all on "off" doesn't mean that the light is off. So the answer wouldn't make any sense. What if the lightbulb was on to start with? Then all the answers would be completely different. If the light bulb was on and hot then it was the switch you never touched. If it was on and cold then it's the one you turned "on"(but actually turned the light off) and then flipped again. And if the light was off, then it was the one you flipped and left in the "on" position.
- Bre (9 Jul 2011)
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