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?

but if you see the light but not the bulb then how do you know which bulb it came from?

Posted by theBal on 2002-05-17 09:49:19