Two trains 180 metres and 200 metres long are running in opposite directions at the speed 40 km/hr and 50 km/hr respectively. In how much time will they cross each other ?

Correct Answer: (D) 15 seconds

Total distance to cross each other is the sum of their lengths: $180$$\text{ m}$ + 200 $\text{ m}$ = 380 $\text{ m}$. Since they run in opposite directions, relative speed is $40 + 50 = 90$$\text{ km/hr}$ = 90 $\times$ $\frac{5}{18}$ = 25 $\text{ m/s}$. The crossing time is $\frac{380}{25}=15.2\text{ seconds}$$\frac{380}{25}$ = 15.2 $\text{ seconds}$, which rounds to 15 seconds (option D).