Delhi Police Constable Exam Model Paper 5

Given:
After 15 years, the child will be three times as old as she was 3 years ago
Calculation:
Let the present age of the child be x.
⇒ Age of child, 3 years ago = x – 3 and Age of child after 15 years = x + 15
According to the question
$\mathit{x}+15=3\times \left(\mathit{x}\mathit{–}3\right)$
⇒ $\mathit{x}+15=3\mathit{x}\mathit{–}9$
⇒ $2\mathit{x}=15+9=24$
⇒ $\mathit{x}=12$ years = present age of child