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?

Asked by Mohit | 26th Apr, 2012, 07:20: PM

Expert Answer:

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

Answered by  | 27th Apr, 2012, 10:26: AM

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