RRB NTPC Prelims Model Paper 5 with solutions

(4) Let the present age of son= x
∴ age of father = 30x After 18 years, the age of father and son will be (30x + 18)and (x + 18) respectively.
∴By question,
$\left(30\mathit{x}+18\right)=3\left(\mathit{x}+18\right)=3\mathit{x}+54$
$\therefore 30\mathit{x}\mathit{–}3\mathit{x}=54\mathit{–}18$
$\therefore 27\mathit{x}=36\therefore \mathit{x}=\frac{36}{27}$
∴ age of father = 30x
$=30\times \frac{36}{27}=40\mathit{y}\mathit{e}\mathit{a}\mathit{r}\mathit{s}.$