A train crosses a pole in 10 sec and a 200m long platform in 20 sec. What is the length of the train? Choose the correct choice from the following
A) 100m  B) 200m  C) 250m  D) 300m  E) 350m
Let the length of train be x meter and speed be y m/sec   Therefore, time taken to cross the pole = x/y sec   and time taken to cross the platform = ( Length of train + Length of platform) / speed of train   Therefore x/y = 10   And, (x+200) / y = 20   ⇒ 10y + 200 = 20 y   ∴ speed of train, y = 20 m/sec   And length of rain = x = 10y = 200m ANSWER : 200m
<result>B</result>
A train crosses a pole in 10 sec and a 200m long platform in 20 sec. What is the length of the train?