Problem:

You are outside a closed room with three switches. Inside the room are three light bulbs. You can turn the switches on and off and enter the room only once. How do you determine which switch controls which bulb?

Scroll to the bottom of the page for the answer

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Solution:

Turn on the first switch, leave it on for a while, then turn it off. Turn on the second switch and leave it on. Enter the room. One bulb will be hot (first switch), one will be on (second switch), and one will be off and cold (third switch).