The distance between Delhi and Agra is 200km a train travels the first 100km at speed of 50km/h how fast must the train travel next 100km so that the average speed is 70km/h for the whole journey

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

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