A 75-metre-long train takes 20 seconds to cross a tree near the railway line. What is the speed of the train in km/h?

Explanation

A train crossing a tree covers only its own length, so the distance is 75 m. Speed = 75/20 = 3.75 m/s. Converting to km/h, 3.75 × 3.6 = 13.5 km/h.