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Number sequence conundrum

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    Number sequence conundrum

    What number comes next in the sequence (and why)?

    20, 3, 5, 12, 15, 4, 30, ?


    Fair warning: I don't know the answer. This question was on a test I took as part of a job application 4 years ago and it was the only one I couldn't solve. After the test, I posed the question to my Facebook friends and they were predictably useless. This morning, Facebook's "past posts" feature threw this shame in my face once again, so I'm hoping one of you can figure it out.

    The test it came from was all math, mostly word problems and number sequences. I would describe the test as notably harder than the typical standardized exams used for entry into American universities, but not overwhelmingly so. It was roughly akin to the latter portion of a Wonderlic Test, if that's any help as a reference. The point is: I don't expect that the numbers are cryptic references to Bible verses or dead presidents. I think it's just a math sequence, and I'm fully prepared to feel foolish upon learning of the solution. Hopefully one of you can make me that fool?
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    Forum Guru xlnitwit's Avatar
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    Re: Number sequence conundrum

    It could be 2, since the product of each prior pair of numbers is 60 (20 * 3, 5 * 12, 15 * 4), so 30 * 2 at the end.
    Don
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    Forum Expert shg's Avatar
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    Re: Number sequence conundrum

    I think xlnw's suggestion is well-observed, but then it's not a extensible sequence.

    It doesn't appear in the OEIS.
    Last edited by shg; 01-12-2018 at 02:06 PM.
    Entia non sunt multiplicanda sine necessitate

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    Re: Number sequence conundrum

    I think 2 might be right! It fits the necessary criteria:
    1) It works
    2) It's reasonably challenging on a timed test (I never thought to view the numbers as pairs) without being truly advanced
    3) I feel foolish for not having seen it

    I wish I had written down the multiple choice options so we could see if 2 was an option. I feel good about the answer though. shg's point is well-taken, but I don't think this particular test aspired to OEIS compatibility. I'd be happy to ponder alternative solutions, but I'm calling it solved. Thank you!

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