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Math Help - Dividing unevenly divisible numbers in the head

  1. #1
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    Dividing unevenly divisible numbers in the head

    Ok this sounds pathetic, and is, but I'm too embarrassed to ask anyone and google was not fruitful.

    Say I want 11/5 and need to do it in my head.

    What formula can I follow?
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  2. #2
    MHF Contributor Amer's Avatar
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    Jordan
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    Re: Dividing unevenly divisible numbers in the head

    maybe 10/5 + 1/5 = 2+1/5 ??
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  3. #3
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    Re: Dividing unevenly divisible numbers in the head

    10/5=2
    1/5=.2
    2+.2=2.2

    Calculator says: 2.2

    Good, so: take the number into an evenly divisible term, divide that by the previous divisor, them divide your remainder by the same divisor and add them?
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  4. #4
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    Re: Dividing unevenly divisible numbers in the head

    the general idea is this:

    say we want to know m/n.

    we first write m = qn + r, where q is the largest integer that "goes into m", when multiplying by n.

    then m/n = (qn + r)/n = (qn)/n + r/n = q + r/n.

    for example, say we want to know 43/7.

    7*6 = 42, and 7*7 is 49, so q = 6. the remainder, r, is 1, so 43/7 = 6 and 1/7.
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