Two trains having lengths of 150 m and 350 m are running at speeds of 60 km/h and 120 km/h, respectively, in the same direction. The time taken (in minutes) by the faster train, coming from behind, to completely cross the other train is:

Correct option is D

Given:
Length of first train = 150 m
Length of second (faster) train = 350 m
First train = 60 km/h
Second train = 120 km/h
Formula Used:

Relative speed =$$v_2 - v_1$$​

Time =$$\frac{\text{Total Distance}}{\text{Relative Speed}}$$​

Solution:

120- 60 = 60 Km/h

Convert speeds to m/s:

​$$60\times\frac5{18} = \frac{300}{18}= \frac{50}{3}$$​m/s

Total distance = 150 + 350 = 500 m

Time =$$\frac{500}{\frac{5}{3}} = 500 \times \frac{3}{50}= 30 sec$$ 

​$$\text{In minutes}= \frac{30}{60} = 0.5 \,min$$​