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Math Help - Subtracting on paper

  1. #1
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    Subtracting on paper

    Hi,

    I have a test paper which I am going through but I am struggling on on question, below.

    I am not permitted to use a calculator.

    Although this would be simple to do in your head, I want to know how I could do it on paper:

    30.00
    0.86

    The answer (yes I cheated, but won't on the actual test) is: 29.14, but I never get this answer when I try and work out this subtraction on paper.

    Could someone explain the technique which I need to use to show it on paper?

    Thank you.
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  2. #2
    MHF Contributor Quick's Avatar
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    Hmm.

    What is 3000 - 86?
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  3. #3
    A riddle wrapped in an enigma
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    Quote Originally Posted by spoosh View Post
    Hi,

    I have a test paper which I am going through but I am struggling on on question, below.

    I am not permitted to use a calculator.

    Although this would be simple to do in your head, I want to know how I could do it on paper:

    30.00
    0.86

    The answer (yes I cheated, but won't on the actual test) is: 29.14, but I never get this answer when I try and work out this subtraction on paper.

    Could someone explain the technique which I need to use to show it on paper?

    Thank you.
    You might want to google a few sites like:

    Cool math Lessons - How to Subtract Decimals (Subtraction)

    Subtraction with Decimals

    to look at a few examples.
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by spoosh View Post
    Hi,

    I have a test paper which I am going through but I am struggling on on question, below.

    I am not permitted to use a calculator.

    Although this would be simple to do in your head, I want to know how I could do it on paper:

    30.00
    0.86

    The answer (yes I cheated, but won't on the actual test) is: 29.14, but I never get this answer when I try and work out this subtraction on paper.

    Could someone explain the technique which I need to use to show it on paper?

    Thank you.
    Quote Originally Posted by Quick View Post
    Hmm.

    What is 3000 - 86?
    This kind of post is the reason I think that calculators are introduced waaaay too early in the Mathematics curricula.

    As quick suggests, write it out like a regular subtraction. Make sure that you put the decimals in line like this:
    Code:
      30.00
      -0.86
    Now forget that the decimal point exists and subtract:
    Code:
      3000
      - 86
      2914
    Now put the decimal point back in:
    Code:
      30.00
      -0.86
      29.14
    -Dan
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