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Why are manhole covers round? What if you get that in a job interview?

en.wikipedia.org — The question of why manhole covers are typically round, at least in the U.S., was made notorious by Microsoft, who began asking it as a job-interview question. Originally meant as a psychological assessment of how one approaches a question with more than one "right" answer, the problem exerts a strange fascination on people.

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  • Switch22, on 10/12/2007, -3/+77For the lazy in all of us:

    Reasons for the shape include: A round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it was inserted diagonally in the aperture (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.) Round tubes are the strongest and most material-efficient shape against the compression of the earth around them. The bearing surfaces of manhole frames and covers are machined to assure flatness and prevent them from becoming dislodged by traffic. Round castings are much easier to machine using horizontal boring mills. Circular covers can also be moved around by rolling, and they need not be aligned to put them back.
    • afghanwhiggle, on 10/12/2007, -4/+23You shoulda just said "so they don't crack sewer workers in the skull."
    • KF6BBL, on 10/12/2007, -1/+95"Circular covers can also be moved around by rolling, and they need not be aligned to put them back."

      Yea but it drives me crazy when they put them back with the yellow stripes going sideways.
    • theone3, on 10/12/2007, -11/+21Pipes are round.
    • qwickone, on 10/12/2007, -8/+24That doesnt mean the manhole cover has to be round. my milk bottle has a round opening, but the bottle itself is rectangular.
    • noodlez, on 10/12/2007, -8/+10article description is inaccurate. there's only one right reason why manhole covers are round, and the parent's is it. thats why they made 'em round, to prevent them from falling down the hole. since they're so heavy, they'd be a pain to get back up, and could kill someone down in the hole if they hit em.
    • bollingj, on 10/12/2007, -34/+3@Switch22
      Man.... you gave this way too much thought!
    • bobothn, on 10/12/2007, -0/+12http://mathworld.wolfram.com/ReuleauxTriangle.html
    • subtle, on 10/12/2007, -3/+18bollingj: No, stupid, he RTFA
    • flowctrl, on 10/12/2007, -6/+13Wow... I would have answered, "because manholes are round".

    • GCRaya, on 10/12/2007, -4/+26That's the problem with the tubes! The square! That's why they are clogged and i didn't get the Internet my secretary sent me.
    • daurkin, on 10/12/2007, -8/+2I thought it was because Microsoft had the patent on the "manhole" and made sure they all had round covers.
    • schlurp, on 10/12/2007, -5/+1Reuleaux triangle? Wouldn't an equilateral triangle do the job?
    • FishPoisonCon, on 10/12/2007, -0/+3doesn't a circle with a radius of 1ft use less material than a 2 ft square?
    • adolfojp, on 10/12/2007, -1/+8You forgot the most important one:

      It requires less material. ;-) You are literally cutting corners.
    • rezonq3, on 10/12/2007, -1/+1Can someone please explain to me the difference in reasoning and whether one is better than the other?

      Switch22's reasons seem logical and well thought out. While that doesn't necessarily mean he is right that those are the reasons they make manhole covers round, it does show that he has thorough analytical qualities.

      To simply say "...Because manholes are round" seems to be an 'easy way out', so to speak. Still that doesn't necessarily mean that ISN'T the reason, it could very well be.

      One side appears to be an objective and 'outside the box' view of why they are round, while the other feels like a clear Ockham's Razor approach to the question.

      Which is right? Both? Neither? Does it really matter? I don't know, can someone give me some idea's?
    • 4NDr01D, on 10/12/2007, -0/+1the doorway's in hobbit houses are round, because they live underground!
    • theone3, on 10/12/2007, -1/+1"That doesnt mean the manhole cover has to be round. my milk bottle has a round opening, but the bottle itself is rectangular."

      Milk isn't round.
  • csmyth, on 10/12/2007, -2/+44Reminds me of that hypothetical feynman interview. Oh, here it is:
    http://hebig.org/blogs/archives/main/000962.php

    "Yes. Round covers are used when the hole they are covering up is also round. It's simplest to cover a round hole with a round cover"
    • gharding, on 10/12/2007, -11/+5Drat. I was just going to post that!
    • JMartin13, on 10/12/2007, -16/+9drat?
    • bass0, on 10/12/2007, -11/+4tard.
    • delcofiftyfive, on 10/12/2007, -4/+2Excellent.
      It took 19 hours to find out that you should put a round manhole cover because the hole under it is round.
  • dawtcalm, on 10/12/2007, -24/+6This isn't a story its a frickin link to wikipedia...
    Whats the point of this post, at least point to a google search for "microsoft riddles" or something. LAME
  • anonymoustroll, on 10/12/2007, -28/+4How fsck should I know... are you interviewing me for a civil engineering position?
  • gotamd, on 10/12/2007, -17/+1It's so they don't fall down the hole. If they were any other shape, they would be able to fall through the hole in the street.
  • medication, on 10/12/2007, -1/+4I actually had this question along with a battery of some half dozen 'open ended' riddles during a job interview once. Working for that company (apparently they liked my answers) was great... until the end of the .com boom.

    I actually like questions along these lines and use them when I interview now. They really do help demonstrate how someone reasons.
  • jo42, on 10/12/2007, -4/+56Q: Why are manhole covers round?

    A: Because manholes are round.
    • mjthom, on 10/12/2007, -16/+1lol *this* is the best answer... gotta love humor like this
    • RickySan65, on 10/12/2007, -0/+5Ever seen a square maintenance guy?
  • NSMike, on 10/12/2007, -4/+18"Goodniiiigghtt, ah-ding ding ding ding..."
    "I... I don't know what to do when you do that..."
    • bobothn, on 10/12/2007, -5/+12Interviewer: Name?
      Stig: What?
      Interviewer: Your name man, your name!
      Stig: Um, er David.
      Interviewer: David. Sure?
      Stig: Oh yes.
      Interviewer: (writing) David Shaw.
      Stig: No, no Thomas.
      Interviewer: Thomas Shaw?
      Stig: No, no, David Thomas.
    • frogpelt, on 10/12/2007, -5/+5Five! Four! Three! Two! One!
    • NSMike, on 10/12/2007, -0/+3For the uninitiated:

      http://www.youtube.com/watch?v=mkj4Wm6INFY

      I love YouTube.
  • trinityrubicon, on 11/10/2007, -9/+15It's like when Steve Jobs, when conducting job interviews, would ask how many times they had dropped acid or when they lost their virginity.
    • biffen, on 10/12/2007, -2/+20No way thats true! Is it?

      I demand linkage.
    • Ramble, on 11/10/2007, -5/+11What a bastard, I'd sue him if he tried that.
    • bobothn, on 11/10/2007, -2/+11i think he is referring to the movie pirates of silicone valley. i am not sure that it ever actually hap pend like that but they say the movie is fairly accurate.
    • marshn, on 11/10/2007, -2/+9Silicone Valley? :D
    • bcore, on 11/10/2007, -2/+15haha pirates of silicone valley... sounds like pr0n. :)
    • Hardcase, on 10/12/2007, -3/+3Silicone Hills, I think.
    • deadbaby, on 11/10/2007, -0/+16It's true. I first read about it in Alan Deutschman's book "The Second Coming of Steve Jobs" (no, it's not erotic fiction. Just a bad title) Someone had brought in a very straight laced guy for an interview. Steve didn't think he was a good fit so he tried to rattle his cage a little. He also writes about an incident where Steve Jobs made a marketing exec cry after some relentless teasing.

      It's an interesting book. Definitely worth picking up.
    • MikeSD34, on 10/12/2007, -0/+4Silicone Valley is between the Silicone Hills, the neighborhoods there are absolutely wonderful.
    • MixedSpleens, on 10/12/2007, -1/+1No, its not like that really. Those questions were ment to jar someone, basicly to be an ass. The mircosoft question is to test how you think, what your logic patterns are.
    • ArcticCelt, on 10/12/2007, -0/+1"It's true. I first read about it in Alan Deutschman's book "The Second Coming of Steve Jobs""

      Yeah I read it too, with a couple of other books on Apple and Steve Jobs and my conclusions are that Steve is a very good business man and particularly an extremely good salesman but a damn scary human resource manager.
    • konspence, on 10/12/2007, -1/+2It's silicon, with no e at the end. Or else there would be no debate over sili-kawn or sili-cone pronunciation.

      Just thought I'd point that out, since all the comments above me have been spelling it wrong.

      (unless you are all doing it as a joke, which I don't get)
    • giantrobot, on 10/12/2007, -1/+1I like this question a lot better: "How many times did you lose your virginity?"

      That is way better than asking how many times you have dropped acid.
  • Petrarch1603, on 10/12/2007, -13/+2there might be a manhole cover in outer space? weird....
  • SteelChicken, on 10/12/2007, -35/+5any time you get a question you dont know the answer too, you say
    "I have no idea, and I would hate to guess. But I would be glad to do the research and provide you with an accurate answer as soon as time permits."

    BOOM your hired.

    • natterca, on 10/12/2007, -3/+47i would never hire someone with that answer.
    • DaveV, on 10/12/2007, -12/+0@natterca:

      Why not?
    • MikeSD34, on 10/12/2007, -0/+13Because it shows the person can't think on the spot. The idea isn't to come up with the right answer based on facts and figures, it's to judge your reasoning ability given what you have in front of you.
    • Salmar, on 10/12/2007, -0/+3I wouldn't either. Maybe with the same sentiments, but without the kissassery.
    • kozie, on 10/12/2007, -0/+4It's not like he asked you, hey there, go do us some research, we wont be paying you.

      It's more like "Answer my question by using your brain, i know it is hard, but please try!"
    • PDubNYC, on 10/12/2007, -0/+3Never. In certain circumstances, such as an interview, they want you to speculate. Not give some lame canned answer.
    • DaveV, on 10/12/2007, -4/+0@MikeSD34:

      I am not so sure about that. The question asks for what is, obstenably, a fact. The person's response was not to guess and not to lie, but to admit that he did not know and would find out.

      On a side note, this kind of question does not really test one's ablity to think on one's feet. It really tests whether one knows the answer and whether one will guess or lie about one's knowledge.

      If one wishes to test an applicant's ablity to think on his feet, one should ask a timed question that requires thinking through a solution. Such a question would be something like:

      You have a fox, a chicken, and a bag of seeds. You have to cross a river. The boat will hold you and only one of the items. The fox will eat the chicken if left together. The chicken will eat the grain if left together.

      How do you get them across the river in as few trips as possible without having anything eat anything else?

      Granted this is a common and well-known puzzel, but there are many like this that can be used.
    • h00paj00, on 10/12/2007, -0/+2Because there's a few set answers already out on the internet and he expects everyone to have memorized techinterview.com's entire website.
    • XStatic, on 10/12/2007, -1/+2Why not just say; Where is a PC, I can Google that for you...
    • ArcticCelt, on 10/12/2007, -2/+5"BOOM your hired."

      ...as the janitor!

      ...and not a very good one.
    • reagan83, on 10/12/2007, -0/+2No! We had someone come in and interview for a developer position and give that response to every question!

      He wasn't hired because he didn't know anything and didn't even want to attempt to solve something on his own so our panel could analyze how his problem solving skills worked.
  • jasorn, on 10/12/2007, -15/+8My wife and I got into a little spat over this. I couldn't understand why should couldn't understand the question. Then we took a trip to her homeland, Thailand. All the manhole covers I saw there were SQUARE. I felt pretty silly. Kinda like M$ brainwashed me for many years into thinking there was only one OS suitable for the desktop :)

    I can already see the replies about how it's not the only OS for the desktop; just the best. Just like the circle isn't the only shape for manhole covers; just the best.
    • airstrike, on 10/12/2007, -5/+4i'm sorry, can you explain one more time how windows is the best OS? there is no 'best OS', there is what you like and what you don't.
    • incongruity, on 10/12/2007, -0/+1There may not be a best, but there are certainly "better" or "worse" by many metrics.
    • neilmarkellis, on 10/12/2007, -0/+3And there are infinite articles on digg discussing this issue, so please not here.
  • conan359, on 11/10/2007, -3/+17This provided me with a great moment. I had a boss in college who liked to prove us wrong, even when we were talking about random *****. Like we saw the old video of the real life(fake) transformer and were talking about how cool it was, he came over and told us it was fake. Good thing cause we had no idea.
    Anyways he found an article about this and then quizzed us with the questions and I gave him this exact answer but he did not believe me and I had to cut example shapes out of paper. He ended up looking like a huge ass in the end. It was a great feeling. Then as soon as he left I went back to sleep.
  • nugge7, on 11/10/2007, -10/+18Eh. You said Manhole.
  • quisxt, on 10/12/2007, -18/+13So a link to a wikipedia article on manhole covers... ...and your summary is one paragraph snipped from the middle of the article. That's front page material now?
    • szembek, on 10/12/2007, -12/+7I also don't fully understand the reason for this 'article'. I thought digg was meant to point to some sort of news, or useful information and hopefully stimulate a conversation about it. The equivalint of this article would be me submitting an article about why I think processed cheese is an awful creation, and link to the wikipedia article for processed cheese.
    • thewaz, on 10/12/2007, -0/+2"equivalint of this article would be me submitting an article about why I think processed cheese is an awful creation"

      sounds worthwhile to me, alot of retards eat that cheese and dont know how bad it is.
  • spokenrope, on 10/12/2007, -12/+7While I was a student at Michigan State for the past couple years, I held two positions that both gave me the opportunity to interview candidates for Night Receptionists on campus. I've conducted well over 100 interviews over the past few years, and my favorite question to ask was always:

    "If you could be any kind of fruit, what kind of fruit would you be and why?"

    I love the question because it shows how well a person can think on their feet, how good they are at thinking critically and imaginatively about something, and communicating those thoughts back to me. Essentially, that question lets me see into a person's soul. :)
    • NSMike, on 10/12/2007, -3/+48I hate you and all interviewers who ask questions like that. Stay out of my soul. I don't want the vaccuum where yours used to be sucking mine in.
    • Otto, on 10/12/2007, -4/+30>>>"If you could be any kind of fruit, what kind of fruit would you be and why?"

      Ham.
      Because fruit sucks.
    • szembek, on 10/12/2007, -10/+13I'd be a cucumber because women are always sti.... oh wait that's a vegetable... ummm I dunno then.
    • ufia, on 10/12/2007, -4/+16@spokenrope: "If you could be any kind of fruit, what kind of fruit would you be and why?"

      I would like to be a potato. What do you mean it's not a fruit? Are you racist?
    • ThatsUnpossible, on 10/12/2007, -7/+9Actually a cucumber is a fruit.
    • 2Wrongs, on 10/12/2007, -3/+6I would regard that question as "Strike One" against your company. I never work for large companies, so for me interviews are one way to learn about the company.

      Those types of questions tell me you don't know how to conduct a technical interview. I'd answer the question (tomacco), but it would set off alarm bells.
    • expunged, on 10/12/2007, -2/+9I might have answered the question, but would have thought twice about taking the job- especially if I had to work directly for you.

      Why would you ask a question like that for a night receptionist position?! In no way is that question relevant to the position being interviewed for. It comes across as a power issue- as if you are getting off on throwing the other person off-balance and asserting your control over the situation.

      Grow up.
    • jlunski, on 10/12/2007, -1/+9Sooo you were looking for quick thinking imaginative NIGHT RECEPTIONISTS? I'm sure the candidates all appreciated your keen sense of humor.
    • MikeSD34, on 10/12/2007, -2/+5Night receptionists deal with all the crazy drunks that accidentially wander in off the streets. No sane person would visit some office building in the middle of the night... So thinking on your feet, definitely an applicable skill.
    • MOJIRA, on 05/17/2008, -0/+1I'd be a pineapple because they're sharp and point on the outside with a cool haircut and make for great drinks on the inside (I'm not sure what that means).
    • innerspirit, on 10/12/2007, -1/+5if I COULD be a fruit, i would choose to not be one, being human is clearly the better choice...
    • russryba, on 10/12/2007, -0/+3The university is obviously starting genetic experiments converting people to fruit. These poor unknowing people were forced to choose their own death. Watch for night staff starting to mysteriously disappear.

      That's why my response would be that I want to remain a Human Bean!

      .. oh... time for my meds
  • mecole21, on 10/12/2007, -9/+16correct answer: God made them that way.
    • neilmarkellis, on 10/12/2007, -4/+4That would work if you were trying to get a job with Bush.
  • subtle, on 10/12/2007, -0/+17>>Formula 1 race cars create so much vacuum due to their aerodynamics that they can lift a manhole cover above the ground. During races on city streets, the manhole covers must be welded down to prevent injury. In 1990, while racing in Montreal, racer Jesus Pareja's car struck a manhole cover that was lifted by the ground effect of the car he was following, causing his car to catch fire.

    So that explains that scene in Sly's crappy racing movie
  • Rikkochet, on 10/12/2007, -1/+20Reminds me of this gimmick a local radio station has, called "Tell us something we don't know."
    They get a bunch of people calling in to tell them some random fact most people don't know, and then give away some tickets. The example they gave one day was just that - why are manhole covers round?
    One lady called and gave some fact about breast size, one dude called about carpet underlay and the third guy was right on the ball.
    "Do you know why they put the manholes right in the lanes on the road instead of in the middle where you don't drive over every one?"
    DJ: "No, why?"
    "JUST TO PISS YOU OFF"
  • EmberX, on 10/12/2007, -1/+5I've actually gotten this in an intervew. I knew the answer because I had heard of this before and the interviewer looked stunned when I knew the answer. Like it says in the article, it's more of a "let's see how they approach a problem" question.
  • nocountries, on 10/12/2007, -16/+7get with the 21st Century - they are called Personhole covers now!
    • szembek, on 10/12/2007, -7/+8Redundant post. Check before you submit.
  • w0nt0n, on 10/12/2007, -0/+5http://www.drainspotting.com/
    Linked FTA and very cool.
    • JeremiahLBurns, on 10/12/2007, -5/+3Jesus, American 'man and/or woman covers' are ugly!
  • marthaphoebe, on 10/12/2007, -2/+18They are round because it's easier to roll off and steal and resell to the same buyers. Which is precisely what the manhole cover manufacturers do. This is how they maintain their revenue stream. C'mon Microsoft, you know you do the same thing. Ok, now hire me.
  • whfsdude, on 10/12/2007, -1/+6Because they're not grates.
  • Mace37, on 10/12/2007, -8/+2Wow, I guess I'd get a job at microsoft pretty easy. I guessed the top 2 reasons off of the top of my head. 1. So they don't fall through the hole, 2. So they're easy to put into place, I didn't think about rolling them though I think that's a load of crap. They weigh over 100 lbs, who's going to put them on their side?
  • ezrider0, on 10/12/2007, -8/+4everyone knows why they're round, at least every engineer. the cover can't fall in!
    • spyrochaete, on 10/12/2007, -4/+11"everyone knows why they're round, at least every engineer."

      As a technical writer I can easily say that this is a very typical engineer viewpoint! Narcissistic and poor grammar!

      I don't mean to pick on engineers - we'd be eating berries and flinging poo without them - but they often become frustrated when I try to coerce them to give sufficient information to make concepts palatable for the layperson. As a non-engineer some blatantly "obvious" stuff like this doesn't occur to me without a lot of thought!
  • diggerphelps, on 10/12/2007, -12/+18To keep the Internet "Tubes" from getting clogged.
    • Vironex, on 10/12/2007, -4/+4It seems every "Tubes" joke gets thumbs-up'd beyond reason.
  • Matic, on 10/12/2007, -5/+6I went on the M$ job interview and I studied two books, How to move mount fuji and Programming Interviews Exposed. I was able to answer all of the lateral thinking puzzles they through at me. They were really impressed because they had no idea that I read those books. However, I didn't get the job because the original position was for a tester, but I did so well on the puzzles they wanted to interview me for engineer. By that time 7 hours had passed by and I was so tired that I almost gave up on the engineer interviews and they weren't very impressed. However, I am glad I didn't get the job because where I am now is a lot better.
    • beervolcano, on 10/12/2007, -5/+21Maybe they didn't hire you because you didn't know the difference between "through" and "threw."
    • Matic, on 10/12/2007, -1/+5threw*
    • frogpelt, on 10/12/2007, -3/+12How do you know where you are now is better if you never worked at MS?
    • nj10ii, on 10/12/2007, -6/+7Maybe they didn't hire you because you were an idiot?
  • oogee, on 10/12/2007, -2/+20A similar approach to disarming an applicant is supposedly used at a medical school in Ontario. Those wishing to enter medical school were asked "When did you last masturbate?"
    I guess applicants who were too shy to answer the question may have trouble listening to patients who complain of embarrassing symptoms.
    Too bad my grades were never high enough for med school, I could have answered that one . . .
    • oblivionboy, on 10/12/2007, -2/+1Another possibility is to weed out those that have a habit of doing it in public like the university library. :)
      .o.
    • neilmarkellis, on 10/12/2007, -2/+1Or the interviewer got off on asking the question?
  • algorhythm, on 10/12/2007, -1/+3Its because construction crews leave round holes in the road. If the manufacturers made any other shape, it wouldn't fit right.
  • warmonger48, on 10/12/2007, -3/+8The two dumbest questions I've been asked in interviews:

    I'm writing a book: 101 uses for a brink. I'm stuck on 100, give me one more.

    If you were any kind of fruit what kind of fruit would I be?
    • marthaphoebe, on 10/12/2007, -3/+11i can't think of even one use for a brink
    • Otto, on 10/12/2007, -1/+30WTF is a brink?
    • beervolcano, on 10/12/2007, -0/+15101. Being the subject of an interwiew question.
    • javakaiser, on 10/12/2007, -1/+3how would you design a toaster?
    • warmonger48, on 10/12/2007, -0/+7sorry, brick...
    • Otto, on 10/12/2007, -0/+12Ahhh! Brick. Well, the answer is obvious.

      101. Beating three kinds of hell out of interviewers who ask stupid questions during interviews.
  • Dycacian, on 10/12/2007, -9/+2So they can never fall into the hole. Square covers can fit into their own hole
    • ThePict, on 10/12/2007, -0/+1Thank you, we've been over this ground a few times now.
  • TheGeek27, on 11/10/2007, -1/+22Because giraffes are not purple.
    • Beanlover, on 10/12/2007, -0/+1Because chickens don't have lips.
    • shotgunhaircut, on 10/12/2007, -1/+1Not even ones between their hips.
  • DarthTurducken, on 11/10/2007, -4/+11The sewer system is a series of tubes too!
    • HoboMaster, on 10/12/2007, -3/+6That explains a lot about the internet.
    • BenBenMan, on 11/10/2007, -0/+1Well, you wouldn't want the sewer system to be a big truck would you?
  • one2gamble, on 10/12/2007, -6/+2so that wiki article doesnt actually answer the question

    The best answer is "because they are"
    • penguin06, on 10/12/2007, -0/+2apparently you didn't read it... it gives about five good answers

      so they don't fall through the hole... easier to manufacture... manholes are round.... easier to move by rolling... etc.
  • sion2119, on 10/12/2007, -13/+2Here is the answer, they are round so they won't fall in the sewers, any other shapes will!
  • haloevo, on 10/12/2007, -10/+3because if they were square or anything else, they would be able to fall down the pipes. This way it is impossible for them to fall in the holes that they cover.
  • Slovenian6474, on 10/12/2007, -9/+2Actually they were made round because they can be rolled away easily and also no matter which way you turn it, it won't fall through the hole.
    • ThePict, on 10/12/2007, -7/+1SHUT UP ALREADY!!! We understand. You're not clever because you can read the comments above you and copypasta.
      Oh, and THIS IS NOT A JOB INTERVIEW. You don't have to answer. (So shut up already)
    • ArcheKlaine, on 10/12/2007, -1/+4ThePict: Copypasta outside of /b/? Nonsense.
  • dprior, on 10/12/2007, -7/+1I have updated Wikipedia with the correct, and most simple answer, which I gave in an interview with Microsoft (admitedly, the question was asked as a joke).

    Manhole covers are round because manholes are round.
  • frogpelt, on 10/12/2007, -8/+3I have a good question for an interview: Why is a link to a wikipedia entry on the front page of digg?
    • psychotron, on 10/12/2007, -0/+1Because it's Digg! The only things that appear in Digg are articles about Digg, Apple Rocks, Ubuntu Rules, and Microsoft Drools. This whole discussion is awesome though because there have been some great answers. Leave it to Digg to accidentally end up with a great discussion where there shouldn't be one.
  • bernierm, on 10/12/2007, -0/+37My answer: "Optimally, they should be cone-shaped, so that a single size cover can fit any size manhole."

    Q: "But what about small manholes? Wouldn't there be a lot of extra manhole cover protruding into the street?"

    A: "That sounds more like a user problem, not a design problem."
  • kamtsa, on 10/12/2007, -9/+3It is a myth that rectangular manhole covers must fall in!

    If you make that step around the edge of the cover wide enough, a manhole of virtually any shape will not fall in.

    Note that round manholes are not cylindrical, they are wider at their top than at their bottom. This can be applied to manhole of any shape. You do the math.
    • protogenxl, on 10/12/2007, -1/+3A^2 + B^2 = C^2 !!!!!!!!!!!!!!!!!

      It is impossible for a round manhole cover to fall through the hole. The Maximum Diameter of a 1.5 foot round Hole Is Constant 1.5 feet no matter what. 1.5 foot wide Square hole has Mamimum Diamaeter that will vary between 1.5 feet and 2.1 feet so you move it Wrong and it is going down.
    • icarus429, on 10/12/2007, -0/+0Actually most manholes are more narrow at the top. And, yes, if you put a big enough lip on the opening, then the cover of any shape is not going fall through. Of course that means the cover has to be larger for the same sized hole. So you end up wasting more material, it's heavy so it's harder to move, etc.
  • bacon_skoda, on 11/10/2007, -2/+11I feel so stupid now after investing money into a local square manhole cover startup.
  • jschlitzer, on 10/12/2007, -1/+0When I was interviewing for my current job six years ago, my interviewer asked me "How many baseball diamonds are in the US?" I was at a lost for words. I was thinking "Why the hell is he asking me this?" and "What does this job have to do with baseball?". I didn't panic, but I'm sure I had a very confused look on my face. He was a nice guy and told me he asked me because he wanted to see what my thought process was like. He wasn't looking for a correct answer, but looking how I derived at my answer.
  • pr0gr4m, on 10/12/2007, -4/+1The fact that other shapes could fall in doesn't answer why the manhole covers are round. It answers why manhole covers aren't square or rectangular. The one correct answer is because the manhole opening is round.
  • inkubux, on 10/12/2007, -0/+11What... is the air-speed velocity of an unladen swallow?
    • penguin06, on 10/12/2007, -0/+640.2 MPH top speed
    • MattElmore, on 10/12/2007, -0/+7African or European?
    • esaks, on 10/12/2007, -0/+1My Chemistry teacher in high school used to put this question on his tests for extra credit.
    • inkubux, on 10/12/2007, -0/+2@MattElmore

      I don't know that aaaauuuuuuuuuuhhhhhhhhhg...

    • koguma, on 10/12/2007, -0/+1How wide is the throat?
  • Skeuomorph, on 10/12/2007, -0/+2Personally, I preferred reading about "Manhole Covers in Space":

    http://www.strangehorizons.com/2002/20021021/manhole.shtml

    • XStatic, on 10/12/2007, -0/+1Crazy talk, the steel plug would have been superheated and ripped apart.

      Lets call it the worlds largest shape charge...
  • ilya2, on 10/12/2007, -1/+3The answer that instantly popped into my mind: "A poisonous one, so no one would eat me."

    Do I have what it takes to be a Night Receptionist?
  • flipmeat, on 10/12/2007, -3/+3Triumph says "The correct answer is who gives a crap!"

    (P.S. correct answer for marketing or management interview)
  • thexder, on 10/12/2007, -3/+1At a recent interview at Citrix I got.

    1. 10 different kinds of things, one kind weighs a 0.1 different, you can only weigh once. Find the different one.
    2. A rope that buns unevenly takes 60 minutes to burn, measure 15 minutes with 2 ropes.
    3. What is the best layout of 500 $1 bills in piles so that you have to give the least amount of piles out when giving out money.
    4. The question about 4 guys with 4 hats, 2 black to white, noone knows their color, two guys can't see anyone else, one guy sees one guy in front of him, one guy sees two guys in front of him. Noone can speak except to say what color hat they have on.

    If they ask you, "How would you move Mt. Fiji?" Don't forget that Mt. Fiji is a volcano.


    I got them all right, but I didn't get the job.
    • jerbaker, on 10/12/2007, -1/+2Whoever asked these questions is a moron. There are myriad logical problems with them.

      #1: 0.1 WHAT?? 0.1 tons, 0.1 milligrams? One is easy to tell without weighing, and one is not.

      #2: One rope burns for 60 minutes, but how long does the second rope burn for?

      #3: This one just defies logic on many levels ... more than I have time to enumerate from work.

      If you have accurately described the questions, they are not possible to answer rationally because critical information is missing. If an interviewer asked me any of these as you worded them, I would probably thank them for their time and leave.
    • thexder, on 10/12/2007, -1/+0I was being vauge.

      1. They all weigh 1lb, except one kind weighs 1.1lbs and you can only perform one weighing on a digital scale. You have an unlimited supply of each kind of thing.

      2. both ropes take 60 minutes to burn, but they burn unevenly, meaning that they don't necessarily take 30 minutes of burning to burn halfway. You have an unlimited supply of matches.

      3. The answer I came up with is using stacks of powers of 2 like in binary/subnetting
      1 2 4 8 16 32 64 128

      4. There is a time element to this I left out, they have 10 minutes to answer, only one has to answer, if he is wrong they all die, if he is right they all go free.
    • ivachen, on 10/12/2007, -0/+2maybe knowing the answer to all these question's answer right on the spot is a dead give away that you read the cheat sheet before going to the interview?
    • thexder, on 10/12/2007, -0/+0I hadn't before the interview. I didn't get the position because during the technical inquisition, my answers, although correct, were not given with enough confidence/certainty. There were a lot of theory questions which I had learned 7 years ago and never used on a daily basis.
    • thexder, on 10/12/2007, -1/+01. Label them a-j, put 1 of a, 2 of b, 3 of c, 4 of d, 5 of e, 6 of f, 7 of g, 8 of h, 9 of i, and 10 of j on the scale. Then wiegh and whetever your decimal remainder is, then it corresponds to the one you put that many of. If the weight is 10.6 then you know it was f that wieghed 1.1lbs. Actually in my question there were only 5 kinds, I put 10 by mistake, and it doesn't work because you could possibly have 10 of j or 10 of a and not know which was which.

      2. Burn one rope on both ends, and start one rope on one end all at the same time. When the first rope(both ends) finishes burning, start burning the other end of the 2nd rope so it is now burning on both ends too. That piece of rope will take 15min to burn.

      3. 1 2 4 8 16 32 64 128 246

      4. Wait for the guy who sees two hats to answer, if he doesn't then the guy who sees one hat knows that his is the opposite of the guy he sees.
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