UPSC 2014 CDS II Math Paper

Let the length of the train be L m and speed of the train be v m/s.
Time taken by the train to cross the pole = 10 s
∴v=

L

10

....(1)  (Speed=

Distance

Time

)
Time taken by the train to cross a 200 m long platform = 20 s
∴v=

L+200

20

........(2)
From (1) and (2), we have

L

10

=

L+200

20

⇒2L=L+200⇒L=200m