A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is

A. 400 m

B. 450 m

C. 500 m

D. 550 m

View Answer

Correct Answer :
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

=> [ x + (x/2) ] / 25 = 12 or (3x/2) = 300 or x = 200

=> 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

=> (200 + y) x (3/40) = 45

=> 600 + 3y = 1800

=> y = 400 m

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