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Math Help - Fractional Formula

  1. #1
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    Fractional Formula

    (1/a)=(1/b)+(1/c)

    Find the value of a if b=3 and c=7

    It has been year since I did any math, Could I please get an explanation of how to solve this problem. Thank you very much.
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  2. #2
    Senior Member yeKciM's Avatar
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    Quote Originally Posted by rms390 View Post
    (1/a)=(1/b)+(1/c)

    Find the value of a if b=3 and c=7

    It has been year since I did any math, Could I please get an explanation of how to solve this problem. Thank you very much.


     \displaystyle \frac {1}{a}=  \frac {1}{b}+ \frac {1}{c}

     \displaystyle \frac {1}{a}=  \frac {1}{3}+ \frac {1}{7}

    multiply all by (21a )

     \displaystyle 21=  7a + 3a  \Rightarrow 10a=21 \Rightarrow a=\frac {21}{10} = 2.1
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  3. #3
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    Quote Originally Posted by rms390 View Post
    (1/a)=(1/b)+(1/c)

    Find the value of a if b=3 and c=7

    It has been year since I did any math, Could I please get an explanation of how to solve this problem. Thank you very much.
    Or...

    \displaystyle\frac{1}{a}=\frac{1}{b}+\frac{1}{c}=\  frac{c}{c}\ \frac{1}{b}+\frac{b}{b}\ \frac{1}{c}=\frac{c+b}{cb}

    \Rightarrow\displaystyle\ a=\frac{cb}{c+b}

    for various values of c and b.
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  4. #4
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    thank you very much
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