Distance between two stations A and B is 778 km. A train covers the journey from A to B at 84 km per hour and returns back to A with a uniform speed of 56 km per hour. Find the average speed of the train during the whole journey.
Sol. Required average speed = `((2xy)/(x + y))` km/hr
= `(2 xx 84 xx 56)/(84 + 56)` km/hr
=` ((2 xx 84 xx 56)/(140))` m/hr = 67.2 km/hr.
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