Two trains one 160 m and 140 m long are running in opposite direction on a parallel track at the speed of 77 km/hr and 67 km/hr respectively. How long will they take to cross each other?

7.5 Sec

Total distance traveled to cross each other = 160 + 140 = 300m

Relative speed in opposite direction = 77 + 67 = 144 km/hr = 144 × \(\frac{5}{18}\) m/sec = 40 m/sec

Time taken to cross =  \(\frac{Total\;Distance}{Relative\;Speed}\) = \(\frac{300}{40}\) = 7.5 Sec.