Two trains, one 125 metres and the other 375 metres long are running in opposite directions on parallel tracks, at the speed of 81 km/hr and 63 km/hr respectively. How much time will they take to cross each other?

12.5 seconds

Relative speed = 81 + 63 = 144 km/h

( when trains moves in opposite direction )

144 km/h = 40 m/sec

Total distance = 125 + 375 = 500 m

Time taken to cross each other = \(\frac{500}{40}\)

= 12.5 sec