I think answer should be 2.4 min

Step-by-step explanation:

method 1

there are two methods which are as follows

Define x:

Let the duration be x

Define the trains:

Let Train A be the train that traveled at 30km/h

And Train B be the train that traveled 35 km/h

Express the distance traveled by train A in term of x

Distance = Speed x Time

Distance = 30x

Express the distance traveled by train B in term of x

Distance = Speed x Time

Distance = 35x

The length of the each train is 200 m.

Therefore, for the train to completely cross each other, Train B (the faster train) will have to be 200 ahead of train A.

Convert 200 m to km

200m = 0.2 km

solve x:

35x - 30x = 0.2 km

5x = 0.2

x = 0.04 h or 2.4 mins

The train will crossed each other in 2.4 mins.

method 2

in image using concept of relative motion ....

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