Two trains 200 m and 150 m long are running on parallel rails at the rates of 40 km/h and 45 km/hrespectively. In how much time will they cross each other if they are running in the same direction?

Two trains 200 m and 150 m long are running on parallel rails

distance = length of the two trains = 200m + 150 m= 350 m

Relative speed by two trains running in the same direction = (45-40)km/m = 5km/hr

time taken for crossing = $$\frac{distance}{speed}$$

we have to change the units of speed  bymultiplying $$\frac{5}{18}$$

                                     =  $$\frac{350 m}{5 \times \frac{5}{18}}$$

                                        = 252 seconds