Question 605207: You are in a lobby of a house. There are three switches all in the off position. Upstairs, there is a room with a lightbulb that is turned off. One and only one of three switches, controls the bulb. you want to discover which controls the bulb, but your are only allowed to go upstairs once.How do you do it?
Answer by bucky(2189)   (Show Source):
You can put this solution on YOUR website! This is more of a logic puzzle than a math problem.
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Throw Switch #1 to the "ON" position, and leave it in that position for a couple of minutes. Then set Switch #1 back to the "OFF" position and quickly throw Switch #2 to the "ON" position. Immediately go upstairs and observe the bulb.
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If the light is on, Switch #2 controls the light because it is the only switch in the "ON" position.
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If the light is off then Switch #2 does not control the bulb. That being the case, feel the bulb. If the bulb is very warm to the touch, Switch #1 turned it on previously, so it (Switch #1) controls the bulb.
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But if the light is off, and it is cool to the touch, then neither Switch #1 nor Switch #2 turned the light on, so the light must be controlled by Switch #3.
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