Given: Length of train A = 60 m Length of train B = 40 m Time taken to cross each other = 10 seconds Formula used: Speed = Distance/Time Calculation: Let the speed of both train is x m/s Relative speed = (x + x)km/h = 2x m/s Now, Time =(60+40)/(2x) ⇒10=100/2x ⇒2x=10 ⇒x=5 m/s ⇒x=18 km/h [1 m/s = 18/5 km/h]