A 250 meter long train crosses a platform in 40 seconds while it crosses a signal pole in 20 seconds. What is the length of the platform?
Choose the most appropriate option
A) 500
B) 1000
C) 350
D) 250
E) 20

Rationale: "speed = [ 250 / 20 ] m / sec = 25 / 2 m / sec . let the length of the platform be x meters . then , x + 250 / 40 = 25 / 2 2 ( x + 250 ) = 1000 è x = 250 m . answer : d"
Answer: D