Multiple choice

A train covers the first half of the distance between two stations at a speed of $40 \mathrm{km} / $ hour the other half at $60 \mathrm{km} / h$. Then its average speed

  1. $48\ km/h$
  2. $50\ km/h$
  3. $40\ km/h$
  4. $60\ km/h$
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A Correct answer
Explanation

Average speed for equal distances is 2*v1*v2 / (v1 + v2). Here, 2 * 40 * 60 / (40 + 60) = 4800 / 100 = 48 km/h.

AI explanation

When equal distances are covered at two different speeds, the average speed is given by the harmonic mean formula 2xy divided by (x + y). Substituting the speeds 40 km/hr and 60 km/hr gives 2 * 40 * 60 / (40 + 60) = 4800 / 100. The average speed is 48 km/hr.

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