Question 12

A train runs between two stations A and B. While running from A to B, its average speed is 60 km/hr and when running from B to A, its average speed is 90 km/hr. The average speed of the train during the two-way journey is

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For equal distances at two speeds, the average speed is $$\frac{2 \times 60 \times 90}{60 + 90} = \frac{10800}{150} = 72$$ km/hr. It is not the simple mean of 60 and 90, because more time is spent at the slower speed.

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