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Thread: find next number in sequence 6, 3, 9, 9/2, 81/4, ....

  1. #1

    find next number in sequence 6, 3, 9, 9/2, 81/4, ....

    okay so, it says what is the next number in the seqence?

    **(important the /'s are frations)**

    6, 3, 9, 9/2, 81/4

    6-3=3
    9-3=6
    9/2-9= 4 1/2
    81/4-9/2= 15 3/4

    uhh??

  2. #2
    Elite Member
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    First, this isn't a math problem. It is a parlor game played in many math classes.
    Second, you need 3-6, not 6-3.
    Third, 9/2 - 9 is negative.
    Fourth, that isn't getting you anywhere, is it?
    Fifth, sequential ratios won't help, either.
    Sixth, since this is just a parlor game, try thinking of something silly, like dividing in half on one step and squaring in the next, then repeating the two steps.

    6/2 = 3

    3^2 = 9

    9/2 = 9/2

    (9/2)^2 = 81/4

    (81/4)/2 = ??

    Seventh, ANY number you can justify should be treated as a correct response. I'm kind of fond of 549/4. I can argue it and motivate it. If someone dared to mark it wrong, they WOULD hear from me.

    Eighth, the REAL answer is -2.

  3. #3
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    Re: find next number in sequence 6, 3, 9, 9/2, 81/4, ....

    Quote Originally Posted by EWallace2012
    what is the next number in the seqence?
    6, 3, 9, 9/2, 81/4
    Here is a website for all these sorts of questions.
    http://www.research.att.com/~njas/sequences/index.html
    “A professor is someone who talks in someone else’s sleep”
    W.H. Auden

  4. #4
    Elite Member stapel's Avatar
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    Quote Originally Posted by EWallace2012
    6, 3, 9, 9/2, 81/4
    As the first tutor suggested, any answer that you can justify (logically, mathematically, etc) should be acceptable (as long as you provide a clear statement of your reasoning). But "the" right answer is whatever the author had in mind when he composed the exercise.

    My guess is that the pattern is an every-other-step sort of thing: divide by 2, square, divide by 2, square, divide by 2, square, .... But your guess, as long as it's sensible, is as good as anybody else's.

    Eliz.

    P.S. Welcome to FreeMathHelp!

  5. #5
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    Divide by two, square.

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