Two trains are in opposite directions with a speed of 50 km/hr and 90 km/hr. Length. Their lengths are 3.6 km and 2.4 km. In what time a slow train cross the fast train.

relative speed of trains are = 50 + 90

                                       = 140 km/hr.

                                        = (140 * 5/18)m/sec

                                        = 350/9 m/sec

Total distance = (3.6 + 2.4)km

                    =  (6.0) km = 6.0 * 1000 = 6000 meter.

Time = (distance/speed)

        =(6000 * 9/350) sec

        = 154.285 sec