Post:

You have three switches in one room and a single light bulb in another room. You are allowed to visit the room with the light bulb only once. How do you figure out which switch controls the bulb? Write your answer in the comments before looking at other answers.


Comment:

If this were an interview question, the correct response would be "Do you have any relevant questions for me? Because have a long list of things that more deserving of my precious time than to think about this!

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[–] 117 points 7 months ago* (5 children)
  • Use the heat of the bulb to determine if it was on. (Shows you can memorize stupid interview questions)
  • Ask a team member to coordinate with you in the other room. (You're a team player)
  • Use a cable locator (Proper tool for the trade)
  • Put your phone in the other room, stream camera feed to your work laptop (The tech approach)
  • Unscrew the bulb. Now you know that no switch controls the bulb (Exposing the flaw in the task's phrasing)
  • Open switch panel and disconnect one switch. Wait a day. If no one complains, disconnect the second. Wait a day. If no one complains, it's probably the third. For good measure, disconnect the third switch. If still no one complains, remove all switches and the lightbulb, since they're not needed anymore. (The Sysadmin approach)
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  • [–] 10 points 7 months ago* (last edited 7 months ago) (2 children)

    What about trying to figure out first what the other two buttons do? Maybe they turn on the light of the room you're in. And I can see light without entering a room right? Just open the door, no need to enter it. If not allowed, look at the foot of the door or try to see if the room has a window.

    No need to buy fancy equipment or even go into the room at all.

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  • [–] 1 point 7 months ago (1 child)

    You're assuming they don't control something in the room with the light, or they could control the lights in your room and the light you're trying to check .

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  • [–] 1 point 7 months ago* (last edited 7 months ago) (1 child)

    Ah yes.
    The infamous "they" who control everything.
    But what "they" who control "they", who are really in control of the lights in your room and the lights you're trying to check?
    What if there's an infinite amount of "theys" all the way down that by mathematical logic leads to myself?
    What if the interview being held and the question being asked wasn't meant to test me, but to test you?
    What then?

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  • [–] 8 points 7 months ago* (1 child)

    Open switch panel and disconnect one switch. Wait a day. If no one complains, disconnect the second. Wait a day. If no one complains, it’s probably the third. For good measure, disconnect the third switch. If still no one complains, remove all switches and the lightbulb, since they’re not needed anymore. (The Sysadmin approach)

    I used this method a few months ago in my breaker box. I needed to make room in it for an EV charger.

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