A train leaves Meerut at 5
a.m. and reaches Delhi at 9
a.m. Another train leaves Delhi at 7
a.m. and reaches Meerut at 10:30
a.m. At what time do the two trains cross each other?

Solution

Train 1 travel time = 4 hours Train 2 travel time is 3.5 = 7/2 hours We know, speed = Distance/time Let the distance b/w Meerut & Delhi is 28 Km (LCM of 4 & 7/2) Speed of 1st train = 28/4 = 7 km/h Speed of 2nd train = 28/3.5 = 8 km/h Relative speed = Train 1 speed + Train 2 speed ⇒ Relative speed = 7 + 8 =  15 km Train 1 travels for 2 hours before train 2 starts. Remaining distance = 28 - 28/2 = 14 km Time is taken to cross each other Time = 14/15 hours or 56 minutes. Total time taken = 2 hours + 56 minutes ∴ They cross each other at 7 : 56 a.m.