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 answers
A) 67.0 km /hr	B) 67.2 km /hr	C) 69.0 km /hr	D) 69.2 km /hr	E) 69.8 km /hr
let us assume A =x,67.2 km /hr=y   distance between two stations a and b=2*x*y= 2xy   but,train cover a journey of   A=56 km/hr 67.2 km /hr=84 km/hr   Average speed =[2xy/x+y]km/hr   = 2*84*56/(84+56) km/hr   =[2*84*56/140] km/hr   = 67.2 km/hr   ANSWER:67.2 km /hr
<result>B</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?