1. ## 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.

2. Originally Posted by rms390
(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 )

$\displaystyle 21= 7a + 3a \Rightarrow 10a=21 \Rightarrow a=\frac {21}{10} = 2.1$

3. Originally Posted by rms390
(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 $b.$

4. thank you very much