Correct Answer - Option 3 : 100 m
Given :
Length of train = LT = 200 m
Length of bridge B = LB = 400 m
Calculations:
Let the speed of train = ST
And Length of bridge A = LA
Formula used :
Speed of train = (length of train + length of bridge) /time taken
ST = (LT + LA )/15 ----(1)
Also , ST = (LT + LB )/30 ----(2)
On equating equation (1) and (2) we get
⇒ (LT + LA )/15 = (LT + LB )/30
⇒ (200 + LA)/15 = (200 + 400)/30
⇒ LA = 100 m