Question

Find the value of $f$ in $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$, when $u=15$ and $v=10$.

• A. $-6$
• B. $\frac{1}{6}$
• C. $6$
• D. $-\frac{1}{6}$

Answer 1

Answer: (C)

$6$

$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$
$u=15,v=10$
$\frac{1}{f}=\frac{1}{15}+\frac{1}{10}=\frac{2+3}{30}=\frac{5}{30}$
$\therefore f=\frac{30}{5}=6$