In a house there are 3 light switches, all in the off position. Each controls one of 3 light bulbs in a room upstairs. You can flip the switches as many times as you want, but you can only go upstairs once to check the bulbs. How do you determine which switch controls which bulb?
Answer
Turn on switch 1 for several minutes, then turn it off. Turn on switch 2 and go upstairs. The bulb that's on is controlled by switch 2, the bulb that's off but warm is controlled by switch 1, and the bulb that's off and cool is controlled by switch 3.