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Math Help - subtraction

  1. #1
    Junior Member
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    subtraction

    When we use the standard subtration algorithum to subtrart
    52
    -19
    _____

    we must regroup. Which property or properties of arithmetic do we use when we regroup?
    Answer this question by writing 52 in expanded form and by using parentheses carefully to show regrouping.

    thank you
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  2. #2
    Super Member Aryth's Avatar
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    Well, we have:

    52
    -19
    -----

    9 cannot be subtracted from 2, so the 5 means 5 tens, we just take one away and make it 10 ones:

    4 12
    (5)(2)
    -19
    ------


    Now, we can completely subtract:

    4 12
    (5)(2)
    -19
    ------
    33

    And there you go.
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  3. #3
    MHF Contributor
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    52 = 50+2 = 5*10 + 2 = (4*10 + 10) + 2 = 4*10 + (10+2) = 40 + 12

    The important step is the bold one. That looks Associative to me.
    Last edited by TKHunny; May 9th 2008 at 01:59 PM.
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