Madhya Pradesh Police Exam Model Paper 2

Calculation:
Fifteen years ago father's age was four times the age his son,
Let the age of son be = x years
∴ Father's age = 4 × x = 4x years
Now, 10 years ago father's age becomes thrice the age of his son
⇒ Son's age 10 years ago $=\mathit{x}+5$
⇒ Father's age 10 year ago $=4\mathit{x}+5$
Now,
⇒ Father's age = 3 × age of son
$\Rightarrow 4\mathit{x}+5=3\times \left(\mathit{x}+5\right)$
$\Rightarrow 4\mathit{x}+5=3\mathit{x}+15$
$\Rightarrow 4\mathit{x}-3\mathit{x}=15-5$
$\Rightarrow \mathit{x}=10$
⇒ Age of son 15 years ago was 10 years, at present his age is 25
∴ After 25 years his age become 50 years.