Question

Tick (✓) the correct answer:
If $\frac{n}{n+15}=\frac{4}{9}$, then n = ?
(a) 4
(b) 6
(c) 9
(d) 12

Answer 1

(d) 12

$$\begin{gathered} \frac{n}{n+15}=\frac{4}{9} \\ \Rightarrow 9n=4(n+15) \\ \Rightarrow 9n=4n+60 \\ \Rightarrow 9n-4n=60 \\ \Rightarrow 5n=60 \\ \Rightarrow n=\frac{60}{5}=12 \end{gathered}$$