Question

Tick (✓) the correct answer:
If $\frac{n}{2}-\frac{3n}{4}+\frac{5n}{6}=21,$ then n = ?
(a) 30
(b) 42
(c) 36
(d) 28

Answer 1

(c) 36

$$\begin{gathered} \frac{n}{2}-\frac{3n}{4}+\frac{5n}{6}=21 \\ \Rightarrow \frac{6n-9n+10n}{12}=21 \\ \Rightarrow 7n=21\times 12 \\ \Rightarrow 7n=252 \\ \Rightarrow n=\frac{252}{7}=36 \end{gathered}$$