There is a lightbulb inside a closet. The door is closed, and you cannot see if the light is on or off through the door. However, you know the light is off to start.
Outside of the closet, there are three light switches.
One of the door light switches controls the lightbulb in the closet. You can flip the switches however you want, but once you open the door, you can no longer touch the switches.
How do you figure out without a doubt which of the three light switches controls the light?
