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Two trains of length 120 m and 280 m are running towards each other on parallel lines at 42 kmph and 30 kmph respectively. In what time will they be clear of each other from the moment they meet?

  • A.14 sec
  • B.21 sec
  • C.17 sec
  • D.20 sec

Answer: D

Trains in the same direction close at the difference of their speeds; in opposite directions, at the sum.

\[ 1 \text{ kmph} = \frac{5}{18} \text{ m/s} \]

\[ \text{relative speed} = 42 + 30 = 72 \text{ kmph} = 20 \text{ m/s} \]

\[ t = \frac{120 + 280}{20} = \frac{400}{20} = 20 \text{ sec} \]

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