Multiple choice

Two trains of equal length, running in opposite directions, pass a pole in 18 and 12 seconds, respectively. In how much time will the trains cross each other?

  1. 14.4 sec

  2. 15.5 sec

  3. 18.8 sec

  4. 20.2 sec
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A Correct answer
Explanation

Let length of each train be L. Speed 1 = L/18, Speed 2 = L/12. Relative speed (opposite) = L/18 + L/12 = 5L/36. Time to cross = Total distance / Relative speed = (2L) / (5L/36) = 72/5 = 14.4 seconds.

AI explanation

Let the length of each train be L; the speeds of the two trains are L/18 and L/12. When moving in opposite directions, their relative speed is the sum of these speeds, which simplifies to (2L plus 3L) divided by 36, yielding 5L/36. The time to cross each other is the total distance (2L) divided by this relative speed, calculated as 2L divided by (5L/36), resulting in 14.4 sec.

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