Two trains one 200 m and 250 m long are running in opposite direction on a parallel track at the speed of 33 km/hr and 57 km/hr respectively. How long will they take to cross each other?

18 sec 

Total distance traveled to cross each other = 200+ 250 = 450m

Relative speed in opposite direction = 33 + 57 = 90 km/hr = 90 × \(\frac{5}{18}\) m/sec = 25 m/sec

Time taken to cross =  \(\frac{Total\;Distance}{Relative\;Speed}\) = \(\frac{450}{25}\) = 18 Sec.