Question

A train travels some distance with speed of 30 km per hour and return with a speed of 45 km per hour calculate the average speed of the train

Answer 1

Let's say the distance is x.
Total distance will be 2x.
Time for first trip = x/30
Time for second trip = x/45

 Average speed = 2x/(x/30 + x/45)
                          = 2x/(x/18)
                          = 36 km/h 

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