Question:
Tick (✓) the correct answer
The value of $\left(3^{-1}+4^{-1}\right)^{-1} \div 5^{-1}$ is
(a) $\frac{7}{10}$
(b) $\frac{60}{7}$
(c) $\frac{7}{5}$
(d) $\frac{7}{15}$
Solution:
(b) $\frac{60}{7}$
$\left(3^{-1}+4^{-1}\right)^{-1} \div 5^{-1}=\left(\frac{1}{3}+\frac{1}{4}\right)^{-1} \div \frac{1}{5}=\left(\frac{4+3}{12}\right)^{-1} \div \frac{1}{5}=\left(\frac{7}{12}\right)^{-1} \div \frac{1}{5}=\left(\frac{12}{7}\right) \div \frac{1}{5}=\frac{12}{7} \times 5=\frac{60}{7}$