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?

Flip 1 switch at a time. When you see the light come on, you've found the correct switch. Just because the bulb is not visible, doesn't mean the light from the bulb isn't.

Posted by page410 on 2002-05-17 07:32:13