Multiple choice

A man on a platform notices that a train going in one direction takes 10 seconds to pass him and another train of same length going in the other direction takes 15 seconds to pass him. If the length of the trains is 200 metres each, then what is the time taken by the two trains to pass one another?

  1. 8 seconds

  2. 9 seconds

  3. 11 seconds

  4. 12 seconds

  5. 15 seconds
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Speed of train 1 = 200m / 10s = 20 m/s. Speed of train 2 = 200m / 15s = 13.33 m/s. When passing each other, the relative speed is 20 + 13.33 = 33.33 m/s. The total distance to cover is 200 + 200 = 400m. Time = 400 / 33.33 = 12 seconds.

AI explanation

First, find the speeds of the two trains by dividing their lengths by the times they take to pass the man, which are 200/10 = 20 m/s and 200/15 = 13.33 m/s. Because the trains are moving in opposite directions, add their speeds to get a relative speed of 20 + 13.33 = 33.33 m/s. The total distance they need to cover to pass each other is 200 + 200 = 400 meters, so the time taken is 400 / 33.33 = 12 seconds, making the result 12 seconds.

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