A $255\text{m}$ long train is running at a speed of $72\text{km/h}$. It crosses a platform of length $745\text{m}$ in:

**Step 1: Convert the speed of the train from $\text{km/h}$ to $\text{m/s}$ **
$$\text{Speed}=72\times \frac{5}{18}=4\times 5=20\text{m/s}$$

Step 2: Calculate total distance to be covered
To completely cross the platform, the train must cover a distance equal to the sum of its own length and the platform's length:

$$\text{Total Distance}=\text{Length of train}+\text{Length of platform}$$

$$\text{Total Distance}=255\text{m}+745\text{m}=1000\text{m}$$

Step 3: Compute the time taken

$$\text{Time}=\frac{\text{Total Distance}}{\text{Speed}}=\frac{1000}{20}=50\text{seconds}$$