A train travellin 48 kmph completely crosses another train having half its length and travelling in opposite direction at 4 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)560 m d)600 m

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