### Distance between two stations A and B is 778km. 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 train during the whole journey.

A. 60 km/hr

B. 30.5 km/hr

C. 57 km/hr

D. 67.2 km/hr

The required average speed given by the formula, $\begin{array}{l}\text{ Average speed }\\ =\Large\frac{2xy}{x+y} \small\mathrm{~km}/\mathrm{hr}\\ \text{Where,}\\ \text{x=84 km/hr}\\ \text{y=56 km/hr}\\ \text{Average speed}\\ =\Large\frac{2 \times 84 \times 56}{84+56} \\ =67.2 \mathrm{kmph} \end{array}$