Answer:
Option E
Explanation:
Time taken to cross a pole = Length pf train / Its speed ⇒20 =lspeed
⇒ speed =l20 ---(1)
Time taken to cross a platform =l+800speed
⇒100 =l+800speed ⇒ speed =l+800100 ---(2)
Time taken to pass through a tunnel =(l+400)60
⇒60 =l+400speed
⇒ speed =l+40060 ---(3)
Equating any two out of three will give us l.
∴ Correct answer is (E).