A 300 metre long train crosses a platform in 39 seconds while it crosses a post in 18 seconds. What is the length of the platform? Choose the correct answer:  A) 150 m  B) 350 m  C) 420 m  D) 600 m  E) 700 m

Rationale: explanation : length of the train = distance covered in crossing the post = speed × time = speed × 18 speed of the train = 300 / 18 m / s = 50 / 3 m / s time taken to cross the platform = 39 s ( 300 + x ) / ( 50 / 3 ) = 39 s where x is the length of the platform 300 + x = ( 39 × 50 ) / 3 = 650 meter x = 650 - 300 = 350 meter answer : option b
Answer: B