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  1. A train travelling at 48 km/hr crosses another train, having half its length and travelling in opposite direction at 42 km/hr, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the railway platform is
    1. 200 m
    2. 300 m
    3. 350 m
    4. 400 m
Correct Option: D

Let the length of the train travelling at 48 kmph be x metres.
Let the length of the platform be y metres.
Relative speed of train
= (48 + 42) kmph

=
90 × 5
m./sec.
18

= 25 m./sec.
and 48 kmph
=
48 × 5
=
40
m./sec.
183

According to the question,
x +
1
= 2
25

= 12
⇒ 
3x
= 12
2 × 25

⇒  3x = 2 × 12 × 25 = 600
⇒  x = 200 m.
Also, 
200 + y
= 45
40/3

⇒  600 + 3y = 40 × 45
⇒  3y = 1800 – 600 = 1200
⇒  y =
1200
= 400 m.
3



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