Problem #3 EASY
The Three Light Switches
Google Adobe Lateral Thinking
Problem Statement
You are standing in a hallway outside a closed room. On the wall next to the door are three light switches, labeled 1, 2, and 3. Inside the room, there is a single incandescent light bulb.
You cannot see into the room from the hallway. You are allowed to flip the switches in any combination and leave them in any position you want. However, you can only enter the room once to inspect the light bulb.
How can you determine with absolute certainty which switch controls the light bulb?
Answer & Quick Explanation
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Turn Switch 1 on for 10 minutes, turn it off, turn Switch 2 on, and enter the room; the bulb will be on (Switch 2), off and hot (Switch 1), or off and cold (Switch 3).
Detailed Editorial Solution
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This riddle requires thinking beyond just the visual state of the bulb (on or off) and utilizing physical properties like temperature.
Here is the step-by-step strategy:
1. Turn Switch 1 ON and leave it on for about 10 minutes. This gives the bulb enough time to heat up.
2. After 10 minutes, turn Switch 1 OFF and immediately turn Switch 2 ON. Leave Switch 3 OFF.
3. Open the door and enter the room.
Now, inspect the light bulb:
- If the light bulb is ON, it must be controlled by Switch 2 (since it's the only one currently on).
- If the light bulb is OFF, touch it carefully:
- If the bulb is HOT to the touch, it must be controlled by Switch 1 (which was on for 10 minutes and just turned off).
- If the bulb is COLD to the touch, it must be controlled by Switch 3 (which was never turned on).