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 56km per hour. Find the average speed of the train during the whole journey?
Choose the correct choice from the following options:
A) 69.0 km /hr	B) 69.2 km /hr	C) 67.2 km /hr	D) 67.0 km /hr	E) 65.0 km /hr
Explanation:   If a car covers a certain distance at x kmph and an equal distance at y kmph. Then,   average speed of the whole journey = 2xy / x+y kmph.   By using the same formula, we can find out the average speed quickly.   Average speed   =2×84×56/84+56 = 2×84×56/140   =2×21×56/35=2×3×56/5   =336/5= 
<gadget id="calculator">336/5</gadget>
<output>336/5 = around 67.2</output>
67.2   Answer: Option 67.2 km /hr
<result>C</result>
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 56km per hour. Find the average speed of the train during the whole journey?