Correct Answer: Option A
Let the length of the first train be x metres.
Then, the length of the second train is (x/2) metres.
Relative speed = (48 + 42) kmph = (90 x (5/18)) m/sec = 25 m/sec.
Therefore, (x + (x/2)) / 25 = 12
Or, 3x/2 = 300
or, x = 200.
Therefore, Length of first train = 200 m.
Let the length of platform be y metres.
Speed of the first train = (48 x(5/18)) m/sec
= (40/3) m/sec.
Therefore, (200 + y) x (3/40) = 45
=> 600 + 3y = 1800
=> y = 400 m.
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