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Math Help - Reducing Fractions Questions

  1. #1
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    Reducing Fractions Questions

    Now when I reduce fractions while multiplying I am getting confused. I know I can cross cancel AND do vertical reduction.

    Now when i do the problem:

    18/12 35/70
    I reduce to
    3/2 1/2


    I then FLIP...cross cancel and multiply like so:


    3/2 • 2/1
    Cross cancel the 2's
    3/1 • 1/1 = 3/1



    This problem is correct. However. When I do the same thing with the following problem, I get an incorrect answer. What am I doing wrong?


    240/10 65/100
    I reduced to
    24/1 13/20


    I then...cross canceled 20 and 24.....flipped...and multiply like so:


    6/1 • 13/5
    Flip and multiply
    6/1 5/13 = 30/13





    that is the wrong answer. it should be 36 and 12 over 13.

    What did I do wrong and why is it wrong?
    Last edited by Jman115; October 31st 2008 at 09:34 AM.
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by Jman115 View Post
    However. When I do the same thing with the following problem, I get an incorrect answer. What am I doing wrong?


    240/10 65/100
    I reduced to
    24/1 13/20


    I then...cross canceled 20 and 24.....flipped...and multiply like so:


    6/1 13/5
    Flip and multiply
    6/1 5/13 = 30/13





    that is the wrong answer. it should be 36 and 12 over 13.

    What did I do wrong and why is it wrong?
    \frac{24}{1} \div \frac{13}{20}=\frac{24}{1} \times \frac{20}{13}

    You cannot "cross/cancel" over division....only multiplication.
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  3. #3
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    Oh duh, thanks a bunch.
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  4. #4
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    Quote Originally Posted by Jman115 View Post
    Now when I reduce fractions while multiplying I am getting confused. I know I can cross cancel AND do vertical reduction.

    Now when i do the problem:

    18/12 35/70
    I reduce to
    3/2 1/2


    I then FLIP...cross cancel and multiply like so:


    3/2 2/1
    Cross cancel the 2's
    3/1 1/1 = 3/1



    This problem is correct. However. When I do the same thing with the following problem, I get an incorrect answer. What am I doing wrong?


    240/10 65/100
    I reduced to
    24/1 13/20


    I then...cross canceled 20 and 24.....flipped...and multiply like so:


    6/1 13/5
    You haven't "flipped" yet! You can't cancel numbers in the two different fractions until after you have flipped them
    24/1 13/20= 24/1 x 20/13 and now the 24= 4(6) and 20= 4(5) are both in the numerator- they cannot be canceled.

    Flip and multiply
    6/1 5/13 = 30/13





    that is the wrong answer. it should be 36 and 12 over 13.

    What did I do wrong and why is it wrong?
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