A 420 meter long train crosses a platform in 60 seconds while it crosses a signal pole in 30 seconds. What is the length of the platform? Answers:
A) 120 B) 840 C) 350 D) 420 E) 210

Rationale: "speed = [ 420 / 30 ] m / sec = 14 m / sec . let the length of the platform be x meters . then , x + 420 / 60 = 14 x + 420 = 840 è x = 420 m . answer : d"
Answer: D