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JAMB Mathematics 1987 Question 5

Question 5

Ratio, Percentages and Rates

A train moves from P to Q at an average speed of 90km/h and immediately returns from Q to P through the same route at an average speed of 45km/h. Find the average speed for the entire journey.

  1. A.55.00km/h
  2. B.60.00km/h
  3. C.67.50km/h
  4. D.75.00km/h
Show the answer and explanation

Answer: B (60.00km/h)

Explanation

Let PQ = d. Time taken = d/90 + d/45 = 3d/90 = d/30. Average speed = total distance ÷ total time = 2d ÷ (d/30) = 60 km/h.