A train speeds past a pole in 10seconds and a platform 50 m long in 20 seconds. Its length is: Choose the most appropriate option:
A) 30 m .	B) 40 m .	C) 60 m .	D) 50 m .	E) 70 m .

Rationale: "let the length of the train be x meters and its speed be y m / sec . they , x / y = 10 = > y = x / 10 x + 50 / 20 = x / 10 x = 50 m . answer : option d"
Answer: D