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Brain Teasers Medium 3 min

A room has three light bulbs and three switches outside the room. Each switch controls exactly one bulb. You may enter the room only once. How can you determine which switch controls which bulb?

Hint
Use heat as well as light.

Answer

Use different heating states before entering.

Explanation

Turn one switch on for several minutes and then off. Turn another switch on and enter. The lit bulb belongs to the second switch, the warm unlit bulb belongs to the first, and the cool unlit bulb belongs to the third.

Step-by-Step Solution

Switch 1 ON for several minutes, then OFF.
Switch 2 ON.
Enter the room.
Lit bulb = switch 2.
Warm unlit bulb = switch 1.
Cool unlit bulb = switch 3.
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