SSC CGL Model Paper 10

Let the speed of Duronto = x km /h
and speed of express train = y km /h
According to the question,
$\frac{720}{\mathit{y}}-\frac{720}{\mathit{x}}=6$
⇒ $\frac{1}{\mathit{y}}-\frac{1}{\mathit{x}}=\frac{1}{120}$ .....(i)
and $\frac{720}{\mathit{x}}-\frac{720}{2\mathit{y}}=2$
⇒ $\frac{1}{\mathit{x}}-\frac{1}{2\mathit{y}}=\frac{1}{360}$ .....(ii)
On solving Eqs. (i) and (ii),
x = 72 and y = 45
∴ Speed of Duronto = 72 km/h