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      Question

      Train A is (35n - 30) metres long, and it is 200 metres

      longer than Train B. Train A takes 20 seconds to pass a tree, while Train B takes 16 seconds for the same. The combined speed of both trains is (3n + 1) metres per second. Find the time Train B will take to cross a platform that is 275 metres long.
      A 27 seconds Correct Answer Incorrect Answer
      B 30 seconds Correct Answer Incorrect Answer
      C 33 seconds Correct Answer Incorrect Answer
      D 24 seconds Correct Answer Incorrect Answer
      E 36 seconds Correct Answer Incorrect Answer

      Solution

      Length of 'B' = 35n - 30 - 200 = (35n - 230) metres

      Speed of 'A' = [(35n - 30) ÷ 20] m/s

      Speed of 'B' = [(35n - 230) ÷ 16] m/s

      (35n - 30)/20 + (35n - 230)/16 = 3n + 1

      4 X (35n - 30) + 5 X (35n - 230) = (3n + 1) X 80

      Or, 140n - 120 + 175n - 1150 = 240n + 80

      Or, 75n = 1,350

      Or, 'n' = 18

      Length of 'B' = 600 - 200 = 400 metres

      Speed of 'B' = (400/16) = 25 m/s

      Required time = (400 + 275) ÷ 25 = 27 seconds

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