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      Question

      Train 'X' can cross a pole in 15 seconds and a 180 metres

      long bridge in 18 seconds. Train 'Y' whose length is 80% of the length of train 'X' runs in the same direction of train 'X'. If train 'Y' crosses train 'X' in 12 seconds, then find the speed of train 'Y'.
      A 185 m/s Correct Answer Incorrect Answer
      B 190 m/s Correct Answer Incorrect Answer
      C 195 m/s Correct Answer Incorrect Answer
      D 200 m/s Correct Answer Incorrect Answer
      E 205 m/s Correct Answer Incorrect Answer

      Solution

      Let the length and the speed of the train 'X' be 'x' metres and 's' m/s.
      ATQ,
      (x/s) = 15
      So, 'x' = 15s.........(i)
      Also, {(x + 180) ÷ s} = 18
      Or, 15s + 180 = 18s [from equation (i)]
      Or, 180 = (18s - 15s)
      Or, 's' = (180/3) = 60
      Length of train 'X' = (15 × 60) = 900 metres
      So, length of train 'Y' = (900 × 0.80) = 720 metres
      Let the speed of train 'Y' be 'y' m/s.
      ATQ,
      (900 + 720) ÷ (y - 60) = 12
      Or, 1620 = 12 × (y - 60)
      Or, (y - 60) = 135
      So, 'y' = 135 + 60 = 195
      Therefore, speed of train 'Y' = 195 m/s

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