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Number sequence problem

  1. Jan 6, 2010 #1

    so i am working on some basic math problems and i get this problem about finding the next number in the sequence, and this is it:

    25, 27, 30, 15, 5, 7, 10 __

    I see the simple solution as +2, +3, divided by 2, divided by 3, +2, +3, divided by 2 and so on...

    So given my possible solution the answer should be 5, right? Wrong. Apparently the solution is -5. I dont see how this can be, unless Im missing something. Could the answer indeed be 5 and the negative is a typo? Any help would put my mind at ease, thanks.

  2. jcsd
  3. Jan 6, 2010 #2


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    Welcome to PF!

    Hi Marco! Welcome to PF! :smile:
    Why divison?

    Why not stay with addition and subtraction? :wink:
  4. Jan 6, 2010 #3


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    Do keep in mind that these kinds questions don't really have a "right" answer. Presumably the author had some rule in mind, but that rule cannot be known from just those 7 points of data. (In fact, it can't be known unless you know every term in the sequence!)

    You shouldn't really feel bad that your guess was not what the author had in mind. But you should be able to field another guess now that you know what the next term actually is
  5. Jan 6, 2010 #4
    I see...for some reason that thought didnt pop into my head cause whenever i look at these sequence problems i tend to over-think. Thanks a lot, this shows me to keep things more simple.

    And thanks for the welcome :biggrin:

    Thanks for your input as well. Seems to me like both can be a viable solution given the data points.
  6. Jan 6, 2010 #5
    yep +2, +3, -15, -10, +2, +3, -15, -10
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