87. 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

✅ The correct answer is option A.
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

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

25
2

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

(200 + y) x
3
= 45

40

600 + 3y = 1800
y = 400 m.