(A) 400 m
(B) 450 m
(C) 560 m
(D) 600 m
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(A) 400 m
(B) 450 m
(C) 560 m
(D) 600 m
Answer: Option (A) 400 m
Explanation:
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.