Question

on a 90km track a train travels the first 30km at a uniform speed of 30km/h. Calculate the speed with which the train should move the rest of the track so as to get the average speed of 60km/h for the entire trip.

Answer 1

Total track = 90 km
Avg speed required = 60 km/hr

So, time of total journey = 90/60 = 1.5 hrs

Journey covered = 30 kms
Speed = 30 km/hr
Time spent = 3030 = 1hour

Journey remaining = 90-30 = 60 km
Time remaining = 1.5-1 = 0.5 hrs
Speed require = 60/0.5 = 120 kms/hr