Correct Answer - Option 3 : 50

**Given;**

The ratio of the length of the train is 2 : 3

**Calculation:**

Let be assume length of the train of A and B is 2x and 3x respectively.

⇒ Speed of train A = 2x/4, Speed of train B = 3x/5

⇒ Speed in same direction = 3x/5 - 2x/4 = 0.10x

⇒ Total time taken to cross each other = (2x + 3x)/0.10x = 5/0.10 = 50 second

**∴ The required result will be 50 second.**