LinkedIn Interview Question: You’re in a room with three l... | Glassdoor

Interview Question

Global Customer Support Representative Interview Mountain View, CA

You’re in a room with three light switches, each of which

  controls one of three light bulbs in the next room. Your task is to determine which switch controls which bulb. All lights are initially off, and you can't see into one room from the other. You may inspect the room only once. How can you determine which switch is connected to which light bulb?
logic, analytical, difficult

Interview Answer

4 Answers


Call the switches 1, 2 and 3. Leave Switch 1 off. Turn Switch 2 on for five minutes and then turn it off. Turn Switch 3 on. Enter the room. If a bulb is on, it's controlled by Switch 3. Feel the light bulbs for heat. The warm bulb is controlled by Switch 2. The bulb that is off and cold is controlled by Switch 1.

Interview Candidate on Jan 7, 2012


Anonymous on Nov 22, 2012


jay on Nov 22, 2012

Break through the wall and physically trace the circuits up the wall, through the ceiling, and up to the dividing wall. Resume with tracing to the lights when you enter the lightbulb room.

Anonymous on Mar 20, 2015

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