arithmetic - two trains are running at 40 kmhr and 20 kmhr respectively in the same direction if the fast train completely passes a man sitting in the slower train in 5 seconds the length of the fast train is - skillgun

Relative speed = 40-20 = 20 km/hr = 200/36 m/s = 100/18 m/s
Time = 5 s
Distance = speed × time = (100/18) × 5 = 500/18 m = 250/9 = 27 7/9 m = length of the fast train