A 120 metres long train is running at a speed of 90 km per hour. It will cross a railway platform 230 m long in ?

Here, speed of the running train is 90 km/hr
And length of the train is = 120 metres
We know that,
When a train crosses through the platform, it cover the distance equal to the length of platform + length of the train
So, the time will taken by the train :

$$\frac{{{\text{Length of train}} + {\text{Length of platform}}}}{{{\text{Speed}}}}$$
$$\eqalign{ & = \frac{{\left( {120 + 230} \right){\text{ metres}}}}{{90{\text{ km/hr}}}} \cr & = \frac{{350 \times 18}}{{90 \times 5}} \cr & = 14\sec \cr} $$