arithmetic - two trains 110 metres and 130 metres long are running in the same direction with speeds of 86 kmhr and 68 kmhr in how much time will the first train cross the second - skillgun

Relative speed of the trains = (86 - 68) = 18 km/hr
= 18 * 5/18
= 5 m/s.
time taken by the trains to cross each other = time taken to cover (110 + 130) m at 5m/sec = 240/5 = 48 sec.