Originally posted by: PowerEngineer
Originally posted by: Descartes
Try this one:
There are three switches in a hallway. One switch controls a light fixture in a room at the far end of the hall. The door to the room is closed, and you can't see whether the light is on or off. You need to find out which of the three switches controls the light. How can you be certain of finding that out, making just one trip to the room?
[edit]I'll tell everyone what answer I gave if no one gets it.[/edit]
Turn one one switch; leave it on for about five minutes, then turn it off.
Turn on a second switch, and go down the hall.
If the light is on, then (obviously) it's switch two. If the light is off but the bulb is warm , then it's switch one. If the light is off and the bulb is cold, then it's switch three.