Question

If $\frac{1}{f}=\frac{1}{p}+\frac{1}{q}$ and $p=2,q=3$, then $f$ is

• A. $2\frac{1}{5}$
• B. $1\frac{1}{5}$
• C. $3\frac{1}{2}$
• D. $3\frac{2}{5}$

Answer 1

The correct option is B $1\frac{1}{5}$

Given, $\frac{1}{f}=\frac{1}{p}+\frac{1}{q}$,
where $p=2,q=3$
$\frac{1}{f}=\frac{1}{2}+\frac{1}{3}$
Taking L.C.M. of $(2,3)=6$, we get
$\frac{1}{f}=\frac{3}{6}+\frac{2}{6}=\frac{5}{6}$
Taking the reciprocals on both sides,
$f=\frac{6}{5}=1\frac{1}{5}$