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You are standing in front of a room with one light bulb inside of it. You cannot see if it is on or off. Outside the room there are 3 switches in the off positions. You may turn the switches any way you want to. You stop turning the switches, enter the room and know which switch controls the light bulb. How?

Illustration for riddle: You are standing in front of a room with one light bulb inside of it. You cannot see if it is on or

You turn 2 switches "on" and leave 1 switch "off" and wait about a minute. Then enter the room, but just before you enter, turn one switch from "on" to "off". Once in the room, feel the light bulb. If it is warm, but off, it has to be the last switch you turned off. If it is on, it has to be the switch left on. If it is cold and is off, it has to be the switch you left in the off position.

Why this works

This riddle cleverly uses both the states of the switches and the properties of the light bulb to determine which switch controls it. By turning two switches on and leaving one off, you create three distinct scenarios: if the bulb is warm but off, it means the last switch you turned off controls it; if it’s on, the switch you left on controls it; and if it’s cold and off, it’s the switch that was never turned on. This method leverages both temperature and light to give you enough information to deduce the correct switch, showcasing a fun interplay of logic and physical properties!

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Common Wrong Answers

“Turn on all three switches, then enter the room.”

If you turn on all three switches, you won't be able to determine which switch controls the light bulb, as you will not know if the bulb is on because of one switch or multiple switches.

“Turn on just one switch and then enter the room.”

By only turning on one switch, you can only determine if that specific switch controls the light bulb if it is on. However, if the bulb is off, you won't know if it’s because the single switch you turned on doesn't work or if it's controlled by one of the other two switches.

“Turn on two switches, then immediately enter the room.”

Entering the room immediately after turning on two switches won't allow you to differentiate between which switch controls the light bulb, as you won't be able to tell if the bulb is on due to one switch or both.

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