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Monday, February 2, 2009

Brain Teaser

I got this logic puzzle from an e-mail from a friend, and spent hours thinking of an answer. It really made me wanna look for an answer. So thought I'd put it here as well.

Imagine you are in a room with three switches. The lamps (bulbs) corresponding to each of them are inside a nearby room. If you are allowed to enter the room with the lamps only once, given that you can turn on/off the switches as you wish, how would you find which switch turns which lamp on/off?

Note that when you are outside the room with the lamps there is no way you could know if the lamps are on or off, and you are allowed to enter that room only once.

Actually, there is a quite simple and logical answer to this. Who could find it?



  1. Is it that you turn two of the switches on, and find out which bulb is not turned on? But that leaves you with two switches and two bulbs.

    I'm stumped.

  2. No mate that wouldn't do.
    You need to identify each of the three switches, not just two, and that by entering the room only once.
    Yes, it can be done.

  3. Switch two bulbs on. Switch one of them off again. Go into the other room. One light will be on (the one you switched on). Out of the two lights that are off, one bulb will be warm (the one you switched on and then off again) and the other one will be cold.


  4. What if one of the lights is wired back to front?

  5. Moses, LOL good idea...
    But, well, let's say these are pretty normal switches. You know the answer now anywayz... :D