A train crosses a pole in 10 sec and a 200m long platform in 20 sec. What is the length of the train?

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