Question

Excluding stoppages, the speed of a train is 120 kmph and including stoppages, it is 50 kmph. for how many minutes does the train stop per hour

Answer 1

Consider a distance $d$. The time taken to cover a distance $d$ is $t_1=\frac{d}{50}$.

If there were no stops the time taken is

$t_2=\frac{d}{120}$.

Thus out of time $t_1$, $t_1-t_2$ is stoppage time. Stoppage time per hour is

$\frac{t_1-t_2 }{t_1} =\frac{\frac{d}{50}-\frac{d}{120}}{\frac{d}{120}} \\ =\frac{70}{50} \;hours\\ =\frac{70*60}{50} \;hours\\ =84\; minutes$