NIACL Model Paper 5 with solutions for free online practice

(b) Let the present age of father and the son is x years
and (75 - x) years respectively.
5 years ago, age of father = (x - 5) years
and age of son = 75 - x - 5 = (70 - x) years
According to the question.
$\left(\mathit{x}-5\right)\left(70-\mathit{x}\right)=750$
⇒$70\mathit{x}-{\mathit{x}}^2-350+5\mathit{x}=750$
⇒$\mathit{—}{\mathit{x}}^2+75\mathit{x}\mathit{—}350=750$
${\mathit{x}}^2-55\mathit{x}-20\mathit{x}+1100=0$
⇒$\left(\mathit{x}-55\right)\left(\mathit{x}-20\right)=0$
∴x = 20, 55
∴Present age of father =55 years