Question

A train cover first half of the distance between two station at the speed of 10/s and the other half at 40/s. Then it's average speed of the journey is.
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Answer 1

Answer:

12

Explanation:

Average speed = (total distance)/(total time)

Let total distance = d

The train covers distance d/2 at 10 m/s, so the time taken for this half of the journey is t1 = (d/2)/10

similarly, t2 = (d/2)/15

So the total time is

t1 + t2 = (d/20 + d/30) = (5d/60)

So avg speed = distance/time

= d/(5d/60) = 60/5 = 12 m/s

Note that the average is not the arithmetic mean of the two speeds (12.5 m/s) as you might expect. It’s lower than that, because you spend more time travelling at the lower speed than at the higher one.