A train is running at the speed of 90 km/hr from A to B at 11 am. At the same time another train is running from B to A at the speed of 80 km/hr. If they are running on parallel tracks and the distance between two stations is 680 km, then at what time will they start to cross each other?

3:00 pm

Distance b/w two station = 680 km

Relative speed in opposite direction = 80 + 90= 170 km/hr

Time = \(\frac{distance}{relative\;speed}\) = \(\frac{680}{170}\) = 4 hours

Train will start to cross each other at = 11:00 am + 4 hours = 3:00 pm