Question

On a 150 km track, a train travels the first 50 km at a uniform speed of 20 km/h. How fast the train must travel next 100 km so as to maintain the average speed of 40 km/h for the whole journey?

Answer 1

[(50*20)+(100*x)]/150=40
then x=(40*150-1000)/100
x=50 kmph

Answer 2

$\sf \pmb{Answer :}$

time =200/60=20/6

average speed=Total distance/Total time

Time taken 50km=5/4

remaining time=20/6-5/4=25/12

speed=distance/time

150*12/25=72

remaining speed=72km/h