Question

To arrive on schedule,a train is to cover a distance of 60km at 72km/hr. If it starts 10min late,at what speed must it move to arrive on schedule?

Answer 1

`90` kilometers per hour

Explanation:

Originally, the train will arrive at the place in:

`(60color(red)cancelcolor(black)"km")/(72color(red)cancelcolor(black)"km""/h")=5/6 \ "h"=50 \ "min"`

Because it starts `10` minutes late, it only has:

`50 \ "min"-10 \ "min"=40 \ "min"=2/3 \ "h"` left to arrive on time.

Therefore, it must go at a speed of:

`s=(60 \ "km")/(2/3 \ "h")=90 \ "km/h"` to arrive on time