Em Holliday

Problem

There are three lights inside a room at the end of a long hall. The switches are at the other end of the hall. The lights are off. You may manipulate the switches and walk down to the room only once. How can you work out which switch controls each light?

Answer

Switch on the first switch and leave it on for ten minutes. Then turn that switch off, turn on the second switch and go down to the room. If the light is on, the second switch works it, if the light is off but the globe is warm the first switch works this light, if the globe is off and cool then the third switch works the light.

Smartiepants answer

Go down and open the door first so you can see into the room!