Question

A train travels first 100 km at a speed of 30 km/h.at what speed should train travels the next 100 km so that average speed of train is 50km/h

Answer 1

answer is
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

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