Distance between two stations A and B is 778km. A train covers the journey from A to B at 84km per hour and returns back to A with a uniform speed of 56km 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
Answer: Option D
Solution(By Examveda Team)
$$\eqalign{ & {\text{Average speed}} \cr & = {\frac{{2xy}}{{ {x + y} }}} {\kern 1pt} {\kern 1pt} {\text{km/hr}} \cr & = {\frac{{ {2 \times 84 \times 56} }}{{ {84 + 56} }}} {\kern 1pt} {\kern 1pt} {\text{km/hr}} \cr & = {\frac{{ {2 \times 84 \times 56} }}{{140}}} {\kern 1pt} {\kern 1pt} {\text{km/hr}} \cr & = 67.2{\kern 1pt} {\kern 1pt} {\text{km/hr}} \cr} $$Related Questions on Average
A. 125 km/hr
B. 75 km/hr
C. 135 km/hr
D. 120 km/hr
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