Question

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

Answer 1

total Distance = 200 km
average speed = 70 km/hr
time taken = 200/70 = 20/7 hr
now, train travels 100 km at a speed of 50 km/hr, time taken to travel this 100 km = 100/50 = 2 hr
now the time left = 17/2 - 2 = 13/2 hr
distance left = 100 km
speed = distance/ time = 15.4 km/ hr