A 300 m long train crosses a platform in 42 sec while it crosses a signal pole in 18 sec. What is the length of the platform?
Select:
A) 287
B) 350
C) 828
D) 277
E) 400

Rationale: "speed = 300 / 18 = 50 / 3 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 42 = 50 / 3 3 x + 900 = 2200 = > x = 400 m . answer : e"
Answer: E