Multiple choice

Two trains A and B are running on parallel tracks in the same direction. Train A which is coming from behind, takes 50 seconds to cross B completely. One person in train A observes that he crosses train B in 30 second. If the speeds of the train A and train B are in the ratio of 2 : 1, what is the ratio of their length?

  1. 7 : 5

  2. 5 : 7

  3. 2 : 3

  4. 3 : 5

  5. 3 : 2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let speeds be 2v and v. Relative speed (same direction) = 2v - v = v. When A crosses B completely: L_A + L_B = v × 50. When person in A observes crossing B: L_B = v × 30. So L_B = 30v, then L_A = 20v. Ratio L_A : L_B = 20 : 30 = 2 : 3. Option C matches.

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