Killer Interview Question: How Much Does This Nail Cost?

This addition to our killer interview questions collection has a definite mathematical flavour. Read on — and don't answer too quickly!

Hammer picture from Shutterstock

Converto is a measurement firm tracking advertising, so it's not surprising that CEO Jeff Zwelling includes a mathematics question in interview rounds. Here it is:

A hammer and a nail cost $1.10, and the hammer costs one dollar more than the nail. How much does the nail cost?

If you quickly blurt out "10 cents", you're not paying attention. (If the nail cost 10 cents, the hammer cost a dollar, which would make it 90 cents more expensive.)

There's only one correct answer here, so it's not a question of how you answer, but how you handle any delay while you work it out. For a coding job, you'd ideally express the solution algebraically.

One CEO Asks This Tricky Maths Question To Size Up Candidates [Business Insider]


    That would be 5 Cents.

    110 = 2x + 100
    10 = 2x
    5 = x
    That question is stupid. It's stupid because it purposely tries to trick you with the form of the sentence. It's purpose is to test analytics, not maths. "Can the candidate interpret data correctly?"

    Last edited 12/05/14 10:44 am

      It doesn't sound stupid to me to test the candidates analytic skills.

      If you have read the rest of the article where he says:
      “They don’t have to get the exact right answer, which is a nickel (five cents), but I want to see them at least have a thought process behind it.”

      why 2x?

        I skipped a step. It's 110 = x (nail) + (x + 100) (hammer).
        I merged the 2 xs together for simplicity of calculation in the next line.

    Call me dumb but I still can't figure out why it would be $0.05.

    Where does the 2X come from?

    Shouldn't the equation be:

    110 = X + 100 ?

    Or for the non-algebra folk like me, who think x is a Letter, not a number

    Rules : Hammer and Nail cost $1.10. Hammer costs $1 MORE than the nail.
    If Nail costs 5c
    AND Hammer is $1 MORE than the nail,
    THEN Hammer is $1.05.
    Result : Hammer $1.05 + Nail 0.05c = $1.10

      Thanks, this is the most helpful explaination (and I'm not being sarcastic).


    The nail is $0.00
    The Hammer is $1.00 with 10% GST :D

    The question never stipulated that there was GST included in the price. So who says you have to be analytical when answering this question. Try thinking outside of the box.

      The question doesn't ask the price, it asks the cost. So if we're going to get tricky, we would have to say that while the price may be $0.05, the price reflects cost plus profit margin. And the price does not include external costs, such as the pollution caused by the factory, or the environmental degradation from the mine.

      I guess if a question isn't really designed to elicit a specific answer, then what the question is really doing is testing the ability of the interviewee to spout bullshit and make it sound convincing. Which I presume is a highly sought after skill in today's job market.

      Odd box where GST applies to hammers but not to nails :)

    The nail cost about $4.50, given my hourly rate, and your stupid question.

      What ? You only make $4.50 an hour? Remember you didn't think to tell us if you took an hour or knew it in 5 seconds..............L.M.A.O.


    The nail will cost as much as it says on the bill. Maybe you should ask accounts.
    Now are you going to ask me a relevant question to this job or are you just going to waist my time with stupid questions?

    If you used 3 nails and one hammer, the price is a lot different.
    3 nails (possibly 5 or 6 counting the holes in my tyre) cost me $250. Thus the first nail might only be $0.05, the next ones becomes prohibitively expensive. Ditto for price of the hammer.

    We call X is price of hammer, Y is price of nail
    We have
    X+Y = 1.1
    X-Y =1
    Mean X+Y = 1 + 0.1 = X -Y + 0.1
    So X+Y = X -Y +0.1
    => 2Y=0.1 => Y=0.05

    So price of nail is 0.05

      I understand your first x + y=1.1
      How ever your next line says x-y=1, well you can not just make y a negative with out making the 1.1 a negative, and the facts that you just misplaced 10 cents somewhere mind boggles me..
      Please explain how this happened

    The real question is how much is a solid and securely built house worth to you? ...

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