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!
maybe dont care. hit all 3 of em. answer is: i have figured out that one of the 3 switches controls the bulb (or not)
You have to report back which individual switch it is such that another person is able to control the light bulb reliably because they know which switch
There is no correct answer. The problem in this comment is this is not your time, it’s the interviewer’s time
What would you say is your weakest bigness?
My penis… Wait… No, I heard that right.
Replace the Lightbulb with a paperclip then flip the switches until you hear the circuitbreaker trip
All three switches are on the same circuit.
The answer is to turn on the first one and wait ten minutes. Then turn it off and flick on the second switch and go and look at the light. If the light is off and the bulb is hot it is the first switch if its off and cold its the third switch and if its on its the second switch.
Hope this helps.
that assumes one of the three switches is able to turn the light on, which is not stated in the question
Only works if it’s an incandescent light, but…
Flip one switch. Wait a few minutes. Flip it off.
Flip the second switch and go into the room.
If the light is on, it’s the switch you flipped most recently. If the light is off but warm, it was the first switch. If it’s off and cold, it’s the switch you didn’t touch.
Only works if it’s an incandescent light
LED and fluorescent lights get hot too, it just takes a bit longer.
Yeah like few hours longer. And if I’m asked that I’ll force the interviewer to sit through until it gets warm
You don’t have to narrate your solution in real time.
You can visit the room once, doesn’t say you can’t swap the bulb for a smart bulb and use your phone to figure it out when it enters pairing mode…
I think I was asked this very question in an interview once. I think I answered something along the lines of ‘If you have a light switch like that here in the office, the first thing I would recommend is calling in an electrician to change and move the switch to the correct room. Why would you have a light switch that controls a light in a different room and apparently two switches that do nothing??’
Got the job.
The bathroom where the switch is prone to get splashed?
Sure, but I would still argue the bathroom light switch should be located, I don’t know, next to the bathroom door? And most definitely there shouldn’t be two totally useless switches there.
I don’t think I would like to work for a company that struggles this much with light switches…
Or with water, frankly. Is the only option for the switch inside the bathroom literally in the sink basin? There shouldn’t be that much splashing in a work bathroom.
Gotta rewatch Alice in Wonderland
I think you mean Alice in Borderland
No one should watch Borderlands.
The Borderlands, on the other hand, is a pretty good found footage horror that I’d definitely recommend
You’re screwed, the bulb is now LED and puts off no heat.
Led bulbs become warm after a few minutes. Not hot, but warm enough to identify if it’s been running.
It’s funny to read the reactions and the people not understanding that programming questions are not enough to judge you. We need people with functioning brains and that usually means problem solving skills. And sometimes the problems are fucking idiotic! Nobody cares about the light switches. We want to see how you think. We want people who don’t give up if they can’t look it up.
You think you’re hot shit because you learnt the latest trendy language? I’ve wasted entire days with people like that because they couldn’t be fucking arsed reading error messages and figuring things out by themselves.
Stupid interview questions show you nothing about how people think. Might as well ask them their astrological animal and blood type
Telling me your blood type or astrological signs is as useful as telling me your certifications and years of experience, these days.
On the contrary, someone can learn a lot from a question like this. If they immediately spit out the answer, then I know that they studied and came prepared to answer common questions like that. If they give a response like the OP, then I know they are an asshole to work with. If they don’t know, do they ask follow up questions or ask for a moment to think can tell me how well they like to work in a group. If they talk about asking a coworker vs researching a solution independently first can tell me how they may react to a brick wall of a problem. Last thing that comes to my mind, is how long they try before giving up. That can be a good indicator for how they treat work meetings - do they push through the task one at a time and in exact order, or do they have the social skills to know when it is time to shut up and move on to the next thing.
The problem is that it sounds like a riddle. In a riddle, you’re traditionally supposed to work within the rules that you’ve been told. So, not thinking outside the box here is not an indication that the person isn’t capable of doing so.
Of course, if I encountered this problem in real life, I’d ask Carol from accounting to check the other room, while I flip the switches. But my instinctive answer was that it is not possible, because I assumed it to be a riddle and the provided rules did not allow a solution.
I’ve wasted entire days with people like that because they couldn’t be fucking arsed reading error messages and figuring things out by themselves.
Everyone has those days. People are not a static value.
Which is why companies here don’t do stupid tests but look if you fulfill some absolute minimum requirements and then look how you do with the team and the job for a week.
That’s a much better question, though! “Here’s a stack trace and the source code. Walk me through where to go from here.”
Most places use at least some open source software, so most places can do this, and if you ask your sys admin team nicely, there’s probably some stack traces available, hot off the prod.
Sure, but I’ve a guy working with me who’s supposed to have ten years xp in the tech we use, and he’s pretty fucking useless.
Meanwhile the young front-end dev who didn’t know any of our tech turns out to learn everything we throw at her after one explanation. Pure tech eval would’ve meant throwing her away after reading her cv.
I’ve wasted entire days with people like that because they couldn’t be fucking arsed reading error messages and figuring things out by themselves.
I’ve had a couple interview tasks that are like “clone this repo and run it. Try to do [action]. Tell us any errors you find and how to fix them”
One of them was some sort of redux app, and the problem was a state mutation. Another one, the CSS had some weird so stuff rendered crazy. Both were pretty easy to track down and fix. You could probably also do something that’s like an error thrown, but people would probably just feed that into an AI now.
Since you can use not mentioned tooling either way, i prefer to use a screwdriver to disassemble the switch and look for what switch is connected.
What if they’re all connected?
Then i get the voltage testing equipment.
The “correct” answer doesnt work for led bulbs. A more modern answer would be why the hell can i only go to the room once!? Or you could get a friend/coworker to go to the room and just observe the bulb. One blink switch one, two blinks switch two etc. Lastly if you know a random switch is controlling a light in another room, why the hell is that switch not labeled if you already knew about it. Like how did this problem even arise in the first place. Also if you just want light in the room right now just turn all 3 on and go to the room.
There is no correct answer. The interviewer wants to see how you approach the problem. You can have the correct answer but still make a bad impression, or you can fail to find the standard solution and still ace this test.
I think of the interviewer ask this specific question they aren’t sophisticated enough to expect anything else than the “correct” answer. The question is so old, stupid, and irrelevant that anyone smart enough to ask actual good interview questions would never lead with this.
IMO questions like this only make sense if you slightly modify them to make the “standard” answer impossible.
Then you see how the candidate reacts to curveballs.
I still think it’s more useful to ask the candidate for a problem they’ve solved in a creative way.
i just look through the keyhole and go ham on the switches
- 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)
I am the sysadmin and I approve this message.
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.
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 .
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?
I’ve seen Rick and Morty. I know what they do. Grab a shovel.
I think if its LED then the heat of the bulb strategy won’t work.
Give it few minutes, they get warm as well.
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.
So, how’s the freezer doing by now?
I’m about to throw up.
Dead serious question: I have only ever worked in the public sector (state level and local municipality) but often see or hear about these seemingly idiotic “interview questions” on television (and obviously memes).
Is this:
- just a meme
- just a joke
- an actual phenomenon in the private sector
If 3, what on earth is its purpose and what could the interviewer possibly find out about the applicant by asking this?
I’m calm.
This is part of a series frequently known as “Microsoft interview” questions. The most famous one is, “Why is a manhole cover round?” They are partially meant to gauge your problem-solving abilities, but more importantly see how you react to a question you did not (and could not) prepare for. They’ve since fallen out of fashion, because it was always a terrible way to gauge roles like software developers.
In the private sector, I once was asked to come up with 12 uses for a kettle. I said make 12 cups of coffee. I didn’t get the job.
In the end it all boils down to heating water
Yeah, but ask a stupid question get a stupid answer!
That’s why you don’t make a 10 figure salary. It can also be used to boil oil to throw on invaders when the office is under siege
Who said anything about plugging it in? Bean someone over the head with it!
I don’t have experience with interacting with these questions in an interview, but I think these questions are supposed to be a test of problem solving ability, which could be relevant in some jobs like programming, I suppose. I still think it’s stupid though.
This question in particular I’m pretty sure has a BS “outside the box” answer, where “outside the box” really means “the question is very misleading and to solve it you have to realize that when we explained this scenario, we heavily implied a set of abstracted rules you could try to solve, but we actually want you to “think outside the box” and come up with a different set of rules that, if you thought we were asking this question in good faith, you would have assumed is obviously cheating”, which isn’t relevant to programming skills and is also just ridiculous.
(I think the answer is :
Tap for spoiler
Turn one switch “A” on, and keep it on for some time. Turn it off, and turn another one “B” on. Go into the room. If the bulb is on, B controls it. If it’s off but warm, A controls it. If it’s off and cold, C controls it. :::)
I think they’re stupid too. Going into an interview is already stressful enough and these types of questions don’t put me into “problem solving” mode. They put me into “brain teaser” mode which is a different type of thinking for me. You know how we nailed these questions when I was in uni? We traded them after our interviews between each other and you just had to pretend you’ve never heard it before. So the main thing people were testing was whether or not the question had made it to them.
For programming, there are so many better ways to test out of the box thinking to me … I think the “what happens when you press a letter into a web browser address bar” or something is better and at least relevant. One that I like is, “there’s an outage in production, how would you go about diagnosing it?” Then as an interviewer I’d reshape the scenario and see where they put their focus and where they give up.
Your answer assumes it is known wether it was off or on in the beginning. I did not see that from the question tbh.
It started when Google started hiring hoardes of people and their interview questions “that only a genius could solve” started leaking. At some point, everyone wanted to work at Google, because they had a slide and free sandwiches and whatnot.
Then, every startup, turtlenecked steve jobs-wannabe started copying those nonsensical questions that only “gifted” people could answer.
It’s definitely a thing, praised by every linkedin lunatic, for finding people who “want to be a part of the family”, are “willing to give it 1100%”, and will do overtime for free to prove they’re “worth it”.
Go in the room, smash the lightbulb. There, now it’s none of the switches.
I think I’ll pass this interview no problem.
Edit: Damn, someone beat me to it. I posted without reading the comments as instructed.
“Do you have any questions for us?”
“You have three engineers in one room. The order comes to let one go. Who do you let go and why?”
“Wut?”
The one that came up with the light bulb question. And if they have to ask why, they should go too.
Best response! I pray I will remember it if I ever get in this situation.
