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Question

on a 60 km track a train covers 30 km with a uniform speed of 30 km/h how fast must the train travel to the next 30 km so as to average 40 km/h for the entire trip?

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Solution

Total distance travelled = 60 km

First 30 km it travels at speed 30 km/h. Time taken = 30/30 = 1 h

Suppose the next 30 km is travelled at speed x km/h. Time taken = 30/x h

Average speed = total distance/total time

=> 40 = 60/(1 + 30/x)

=> x = 60 km/h


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