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      Question

      A train of length (Q + 30) metres passes a pole in 18

      seconds and a tunnel of length 540 metres in 36 seconds. Find the time (in seconds) the train will take to cross a bridge of length '2Q' metres.
      A 33 secs Correct Answer Incorrect Answer
      B 45 secs Correct Answer Incorrect Answer
      C 52 secs Correct Answer Incorrect Answer
      D 25 secs Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ,

      Speed of train = [(Q + 30) ÷ 18] m/s

      Also, speed = [(Q + 30 + 540) ÷ 36]

      So, [(Q + 30) ÷ 18] = [(Q + 570) ÷ 36]

      Or, [(Q + 30) ÷ 1] = [(Q + 570) ÷ 2]

      Or, 2 × (Q + 30) = Q + 570

      Or, 2Q + 60 = Q + 570

      Or, Q = 510

      Speed = [(510 + 30) ÷ 18] = 540 ÷ 18 = 30 m/s

      Length of train = Q + 30 = 540 metres

      Required time = (540 + 2 × 510) ÷ 30 = 1560 ÷ 30 = 52 seconds

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