A 400 m long train takes 36 s to cross a man walking at 20 km/h in the direction opposite to that of the train. What is the speed of the train?

Relative speed of train = 400/36 m/s = 400/36 x (18/5) = 40 km/h Relative speed of train = Speed of train + Speed of man ⇒ 40 = Speed of train + 20 ∴ Speed of train = 40 - 20 = 20 km/h