A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

Speed = 72 kmph = 72 × (5/18) = 20 m/s. Train crosses a man in 18 seconds, so train length = 20 × 18 = 360 m. Train crosses platform in 30 seconds, so distance covered = 20 × 30 = 600 m. Platform length = total distance - train length = 600 - 360 = 240 m. The key insight is that crossing the man gives the train length, and crossing the platform gives train + platform length.