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    • Question

      Two trains ‘P’ and ‘Q’ of lengths 600 metres and

      400 metres respectively are travelling towards each other. Ratio of speed of ‘P’ to ‘Q’ is 4:1. If the trains take 50 seconds to cross each other from the time they meet, then find the average of speeds (in km/h) of trains ‘P’ and ‘Q’.
      A 24 km/h Correct Answer Incorrect Answer
      B 27 km/h Correct Answer Incorrect Answer
      C 36 km/h Correct Answer Incorrect Answer
      D 42 km/h Correct Answer Incorrect Answer
      E 54 km/h Correct Answer Incorrect Answer

      Solution

      Let the speed of ‘P’ and ‘Q’ be ‘4y’ and ‘y’ m/s respectively.
      Relative speed = 4y + y = ‘5y’ m/s
      ATQ,
      5y × 50 = 600 + 400
      ⇒ 250y = 1000
      ⇒ y = 4
      Therefore, required average = (4y + y) ÷ 2 = 2.5y
      = 2.5 × 4 = 10 m/s = 10 × (18/5) = 36 km/h

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