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.

160 km/hr
230.5 km/hr
357 km/hr
467.2 km/hr

Answer:- 1

Explanation:-

Solution:

\begin{aligned} The required average speed given by the formula, \\ Average speed = [\frac{2 x y}{(x + y)}] k m / h r \\ Where, \\ x = 84 k m p h \\ y = 56 k m p h \\ Average speed \\ = [\frac{(2 \times 84 \times 56)}{(84 + 56)}] \\ = 67.2 k m p h \end{aligned}

$\eqalign{ & {\text{The}}\,{\text{required}}\,{\text{average}}\,{\text{speed}}\,{\text{given}}\,{\text{by}}\,{\text{the}}\,{\text{formula}}, \cr & {\text{Average}}\,{\text{speed}} = \left[ {\frac{{2xy}}{{\left( {x + y} \right)}}} \right]km/hr \cr & {\text{Where}}, \cr & x = 84\,kmph \cr & y = 56\,kmph \cr & {\text{Average}}\,{\text{speed}} \cr & = \left[ {\frac{{\left( {2 \times 84 \times 56} \right)}}{{\left( {84 + 56} \right)}}} \right] \cr & = 67.2\,kmph \cr}$