Multiple choice

A train crosses a 400 m-long platform in 50 seconds. It crosses another 600 m-long platform in 60 seconds. What are the length and the speed of the train?

  1. $600 m, 72 km/h$
  2. $550 m, 75 km/h$
  3. $500 m, 70 km/h$
  4. $650 m, 74 km/h$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let L be train length, S be speed. For 400m platform: (L+400)/50 = S. For 600m platform: (L+600)/60 = S. Equating: (L+400)/50 = (L+600)/60. Cross-multiply: 60(L+400) = 50(L+600). 60L + 24000 = 50L + 30000. 10L = 6000, L = 600m. Speed = (600+400)/50 = 1000/50 = 20 m/s = 20×(18/5) = 72 km/h. Option A is correct. Option B(550m, 75 km/h), C(500m, 70 km/h), and D(650m, 74 km/h) don't satisfy the equations.

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