The year is 1985. You are on the ground floor of a four-story building. On the top floor there is a lightbulb. On the ground floor with you there are three light switches. All three switches are connected to electricity but only one of the switches controls the lightbulb on the top floor - the other two switches are not connected to anything.

You cannot go outside, there is no one helping you, and most importantly, you can only go up to the top floor one time to check.

How do you determine with absolute certainty which of the three switches controls the lightbulb?

If this post gets any traction I’ll post the answer.

The answer involves no wordplay, is not cheesy or impossible to figure out… just use logic and you should be able to come up with the correct answer.

  • WVbrU@lemmy.worldEnglish
    6·
    17 days ago
    Answer?

    Assuming you know all switches start in the off position: Turn the left switch on and leave it for a while. Then switch it off and turn the middle switch on. Go upstairs.

    If the light is on, the middle switch controls it.

    If the light is off, feel the bulb. If it is warm, then the left switch controls it. Otherwise, the right switch controls it.

    It’s funny you have to specify the year, now that LED bulbs are becoming the norm! (and CFLs before them)

    • UmeU@lemmy.worldOPEnglish
      3·
      16 days ago

      Ding ding ding, good job!

      Tap for spoiler

      Specifying the year might have been too much of a hint but I told this to my 9 year old niece and she immediately said ‘but what if it was an LED bulb?’.

      I had always told this riddle without specifying a year and it always seems to stump people.

  • mutilated_sphincter@lemmy.worldEnglish
    2·
    16 days ago

    ::: spoiler You turn on the first switch and leave it on for an hour, then you turn it off and turn on the second switch. You rush up the stairs - if the bulb is hot, it’s the first switch. If the bulb is bright it’s the second switch, if it’s neither it’s the third switch!

    :::