Question

The distance between Delhi and Agra is 200km.A train travels the first 100km at a speed of 50km/hr.How fast the train travel the next 100km,so as to average 70km/hr for the whole journey?​

Answer 1

Given :

The total distance= 200km

let total time be 't ' hours

speed of train for the first 100 km is 50km/h

time taken for the first 100km(t1)=distance/ speed = 100km/50km/h=2hours

Average speed=total distance/total time taken

=total distance(s1+s2)/total time(t1+t2)

where, s2= next 100km traveled by train.

t2=time taken to travel next 100km

∴70km/hr=200km/(2+t2)hours

70=200/2+t2

140+70t2=200

70t2=60

t2=60/70

t2=6/7 hours.

∴speed required by train to travel next 100km so as to attain 70km/h average speed is:

speed(v2)=distance/ time

=100km/6/7

=700/6

=116.67km/hr