Killer Interview Question: How Much Does A Nail Cost?

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This week's KIQ will take you back to school. How good are you at mathematics these days?

Most of us probably don't have to use maths skills on a daily basis but they may actually come in handy at a job interview, even if the position you've applied for has nothing to do with numbers.

Jeff Zweling is the co-founder and CEO of ZipRecruiter, a job search engine, and he often throws trick maths questions at job candidates. For example, one of the questions he has been known to ask 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?"

This math problem is one of those annoying trick questions that I remember from my high school days. But Zweling isn't exactly expecting you to be a maths whiz. He explained the reason behind his curve ball maths questions:

"Some candidates will instantly blurt out 10 cents, which is obviously wrong. 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.   "… If the person is hired, he or she will eventually have to sit across the table from top CMOs and will need to be able to answer the tough questions that come at them, to think on their feet, and to feel confident in their responses."

How would you tackle this question? Let us know in the comments.

[Business Insider]


    Can someone explain this to me? Apparently I'm a tad thick.

    Hammer (H) + Nail (N) = $1.10
    H = N + $1.00
    Substituting for Hammer
    N+ $1.00 + N = $1.10
    => N + N = $1.10 - $1.00
    2N = $0.10 or N (Nail) = $0.05

      Still lost, nowhere does it mention a second nail;

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

      The bolded words are all singular.

        There's only the one nail, yes.

        Mathematically, there's a relationship between the hammer and the nail: we know the hammer costs a dollar more than the nail. So rewording things in the perspective of the nail, hammer = nail + $1.00.

        So instead of saying "Hammer + Nail = $1.10" we can subsitute the concept of the hammer with the "hammer = nail + $1.00" above, which changes the equation from "Hammer + Nail = $1.10" to "(Nail + $1.00) + Nail = $1.10". From there you just reduce things down mathematically - by subtracting $1.00 from both sides of the equation, for example - to get to "Nail + Nail = $0.10"... which means that (mathematically, remember) each "Nail" equals $0.05.

        That's all chris has done above.

        There's still only one (physical) nail, but maths is a magical world of wonder.

        Last edited 07/11/16 3:52 pm


    Let's work backwards.

    A nail costs 5c
    A hammer costs $1 more than the nail. Which makes it $1.05.
    Therefore, a nail and hammer will cost $1.10.

    Hope that helps!



    P.S. I'm shocking at answering these questions as well. I'd be one of those people who just blurt out "10c!"

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