Two trains, one 390 metres and the other 250 metres long are running in opposite directions on parallel tracks, at the speed of 78 km/hr and 66 km/hr respectively. How much time will they take to cross each other?

Correct option is B

Given:
Length of first train = 390 metres
Length of second train = 250 metres
Speed of first train = 78 km/h
Speed of second train = 66 km/h
Formula Used:
Relative Speed = Speed1 + Speed2 (since trains are moving in opposite directions)
Time taken to cross = (Sum of lengths of trains) / Relative speed
Solution:
Relative speed = 78 + 66 = 144 km/h = 144 × (1000 / 3600) m/s = 40 m/s
Total distance to be covered = 390 + 250 = 640 metres
Time taken = 640 / 40 = 16 seconds.