Answers

2015-01-07T14:06:36+05:30
      train (l)                      platform (200)
<---------------------><-------------------------------------->  
|.............................|..........................................|pole

let the length of train is l meter and speed is v m/s

distance = speed×time
time = 20s
distance = (l+200) m
speed = v
l+200 = v×20  ----------------------------(1) 
apply the same equation again for the pole
now 
distance = l m
time = 10s
speed = v
l = 10×v 
v = l/10 
putting the value of v in equation (1)
l+200 = (l/10)×20
l+200 = 2l
2l-l = 200
l = 200m
so the length of the train = 200m

0