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Math Help - ratios

  1. #1
    Senior Member sfspitfire23's Avatar
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    ratios

    Find A:B, if (2A+4B)/(2A-4B) =3/2

    I start with 2A+4B=3A-6B...
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  2. #2
    Super Member Bacterius's Avatar
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    Find A:B, if (2A+4B)/(2A-4B) =3/2
    I start with 2A+4B=3A-6B...
    Hello,
    (scratch what was there before)

    You could just cross-multiply :

    2(2A + 4B) = 3(2A - 4B)

    Then expand :

    4A + 8B = 6A - 12B

    Simplify :

    20B = 2A

    Simplify again :

    10B = A

    Finally :

    10 = \frac{A}{B}

    Does it make sense ?
    Last edited by Bacterius; July 26th 2010 at 06:37 AM. Reason: edited from mistake
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  3. #3
    MHF Contributor Also sprach Zarathustra's Avatar
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    2a+4b=3

    &

    2a-4b=2
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  4. #4
    MHF Contributor
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    Quote Originally Posted by sfspitfire23 View Post
    Find A:B, if (2A+4B)/(2A-4B) =3/2

    I start with 2A+4B=3A-6B...
    which is fine as the numerator is one and a half times the denominator.

    then 2A-2A+4B=3A-2A-6B\ \Rightarrow\ 4B=A-6B

    4B+6B=A+6B-6B=A

    10B=A\ \Rightarrow\ 10=\frac{A}{B}\ \Rightarrow\ A:B=10:1


    Or...

    \frac{2A+4B}{2A-4B}=\frac{3}{2}\ \Rightarrow\ \frac{2(2A+4B)}{2A-4B}=3

    \Rightarrow\ 4A+8B=3(2A-4B)\ \Rightarrow\ 4A+8B=6A-12B

    20B=2A
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  5. #5
    Super Member Bacterius's Avatar
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    Thanks Archie, for making me notice a typo in my post (fixed by the way). Enough math for me for today - too much mistakes.
    Nice working also
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