Multiple choice

The 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 56 km per hour. Find the average speed of the train during the whole journey.

  1. 67.2

  2. 76.2

  3. 66.1

  4. 70
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A Correct answer
Explanation

Average speed = 2 * v1 * v2 / (v1 + v2) = 2 * 84 * 56 / (84 + 56) = 9408 / 140 = 67.2 kmph. The distance is irrelevant as long as the route is the same.

AI explanation

Since the train travels the same distance in both directions, use the average speed formula for equal distances: two multiplied by the first speed multiplied by the second speed, all divided by the sum of the first and second speeds. Substituting the given values gives two multiplied by 84 multiplied by 56, divided by the sum of 84 and 56. This simplifies to 9408 divided by 140, which equals 67.2 kmph. The average speed of the train during the whole journey is 67.2.

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