Question
A person went from A to B at an average speed of x km/hr and returned from B to A at an average speed of y km/hr. What was his average speed during the total journey ?
Answer: Option D
Answer: (d)
Using Rule 5,
Required average speed = $({2xy}/{x + y})$ kmph
[Since, can be given as corollary If the distance between A and B be z units, then
Average speed = $\text"Totaldistance"/ \text"Time taken"$
= ${z + z}/{z/x + z/y}$
= $2/{1/x + 1/y} = 2/{{x + y}/{xy}} = {2xy}/{x + y}$
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Answer: (d)
Using Rule 5,
Required average speed = $({2xy}/{x + y})$ kmph
[Since, can be given as corollary If the distance between A and B be z units, then
Average speed = $\text"Totaldistance"/ \text"Time taken"$
= ${z + z}/{z/x + z/y}$
= $2/{1/x + 1/y} = 2/{{x + y}/{xy}} = {2xy}/{x + y}$
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