The three switches puzzle: Solution

Are you as smart as a Norwegian crime writer? Have you had a lightbulb moment and solved Alex's classic Three Switches puzzle? Here's the solution.

The Guardian on YouTube:

[Xevronixussor]

My first solution was: turn on the first siwtch... and wait 2-3 years. Then switch on the second, and go upstairs. If the bulb is on, it was the 2nd switch, if its burnt out, it was the first swithch, otherwise the 3rd. Similar, I guess. Then on htis thought I soon came up with the solution mentioned in the video.

[marcustang]

Nowadays people use LED light bulbs that do not emit heat and save energy...that would be a problem for him when he's up there and the bulb is not warm...

[spludgey]

I think this puzzle is unsolvable as it's missing one piece: It needs to also tell us that we know that the lamp is off to start with, otherwise we could switch switch A on for a while, then switch it off and switch switch B on and go up to see the lamp on. We would then incorrectly deduce that switch B controls the light, when it's actually switch C and it's been wired the wrong way around.

[babysealavenger]

I personally would just flip the switches on one at a time and see which one turns the basement light on (the room I'm standing in), then turn it off. Now I know it's one of the two other switches, flip one and go upstairs and see if light is on or off.

If none of the switches connect to a light in the basement, then forget about the whole thing, you probably won't be able to find the wall panel in the dark anyways. Go upstairs and fire your building contractor.

[petraroza]

I assume ! This is the simplest solution is to have each button is on.

---
Feltételezem ! Ez a legegyszerűbb megoldás az, hogy minden gomb be van kapcsolva .

[invisibleman]

Since he never said I couldn't have help, he never said I couldn't hear through the door, and I didn't want to touch a warm bulb. I had a friend I trust go up the stairs and tell me when the light comes on.

[PearlJamLver]

Got it but a slightly different way. You just turn on number 1 for few minutes then turn it off, then turn on nr 2 and go upstairs. If it's turned on its nr 2. If it's turned off but warm its nr 1, or if it's turned off and cold it's nr 3.

[yumo]

I was thinking you'd just switch one on for a few minutes and then turn it off and turn the second one on. So if it's hot it's the first one, if it's on its the second and if it's neither it's the third.

[ticeludo]

Since I cant go back from attic, when I try switches, I'm going to the rest of the house to check lights. Since I discover what switch one of them, I'll now what is attic light switch.

[B.Evil.C]

Thing is, I solved this by using logic and then physics. I have 3 switches but logic indicates I need 3 different states. How can I get 3 states from the bulb...which is Physics.

This problem is going to fail as time goes on.

[gabor_sikler]

And what if, that one of the switces drive the lamp in the downstairs? If one of them makes light in the downstairs, you have only two switches to choose. And that is simple.

[dancoulson]

Turn on switch B and wait a minute.
Turn off switch B, and turn on switch A.
Check the lamp
On = A
Off but hot = B
Off and cold = C

[Donttreadonme]

This isn’t the answer to the original problem. You have to know with 100% certainty before going up the stairs. This, you can’t go to the light to get the answer

[Observer]

Rarely do houses have switches that do nothing!  How about just flipping switches to see what they *do* control downstairs.  If they are downstairs, then there is a high probability that the others control some lights or outlets that you can see.  Gotta think out of the box more...

[iwonder]

I really, really hate this answer. If it's a real life problem and i can actually physically interact with things, I'd tell whoever made the rules to f**** off and just try them one by one. That's much smarter than getting a ladder and check if the bulb is warm.

[bojanmilovanovic]

Ok, lets make it more interesting. Same problem but you can not touch the bulb. Which of those 3 switches lights the bulb? a) switch number 1 b) switch number 2 c) switch number 3 ( from left to right) How about this problem?

[giraysekerlen]

he should explicitly point out whether we are allowed to touch the attic or or not. otherwise we would be thinking out of the context.

[reazorgb]

pointless . On the assumption (because there is no specification) based on that the burner heats. What if there's a burner which does not heat up or cool down faster than than should check it.

[odditoriumleviathan]

Haha, I said quickly run upstairs and see if it has a small glow 😆 but after that was rejected I figured it out.

[MGmirkin]

Yep, solved it on my own many moons ago...