UPSC 2016 CDS II Math Paper

Let the length of the faster train be x m and the length of the platform be y m.
∴ Length of the slower train =

x

2

m
Speed of the faster train with respect to the slower train
=25m/sec
∴x+

x

2

=25×12
⇒

3x

2

=300
⇒x=200
Length of the faster train = 200 m
Speed of the faster train =48×

5

18

=

40

3

m/s
∴200+y=

40

3

×45=600
⇒y=600−200=400
Thus, the length of the platform is 400 m.