Question

39. The distance between Delhi and Agra is 200 km. A train travels the first 100 km at a speed of 50 km/h. How
fast must the train travel the next 100 km, so as to average 70 km/h for the whole journey?
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Answer 1

Answer:

Time taken to travel first half distance = 100/ 50 = 2 hrs

Time is taken to travel second half distance = 100/v

Average speed = 200/ (2 + 100/v)

70 = 200/ (2 + 100/v)

2 + 100/v = 20/7

100/v = 20/7 – 2 = 6/7

v = 100 * 7/6 Km/h

v = 700/6 km/h