Multiple choice

Two trains are coming from opposite directions cross each other in 12 seconds. If the length of the first train and the second train are 1 less than the square of the product of the first and fourth prime number and square of the product of the second and third prime number respectively, and the speed of the first train is 54 kmph, then find the speed of the second train.

  1. 65 kmph

  2. 68 kmph

  3. 60 kmph

  4. 72 kmph

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

First 4 primes: 2, 3, 5, 7. First train length = (2 × 7)^2 - 1 = 196 - 1 = 195m. Second train length = (3 × 5)^2 = 225m. Total length = 420m. Crossing time = 12s, so relative speed = 420/12 = 35 m/s = 126 kmph. Since speed of first train is 54 kmph, speed of second = 126 - 54 = 72 kmph.

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