RRB NTPC 2014 Paper

(2) Let the distance between Ram's house and office be d km. Now,Time taken to travel the distance at5 km/h =$\frac{\mathit{d}}{4}$
Time taken to travel the distance at 5 km/h =$\frac{\mathit{d}}{5}$
Difference between the times taken= 10 + 5 = 15 minutes
15 minutes = $\frac{15}{60}=\frac{1}{4}\mathit{h}$
According to the question,
$\frac{\mathit{d}}{4}-\frac{\mathit{d}}{5}=\frac{1}{4}\Rightarrow \frac{\mathit{d}}{20}=\frac{1}{4}\Rightarrow \mathit{d}=5\mathit{k}\mathit{m}$