A $335\text{ metres}$ long train crosses a pillar in $18\text{ seconds}$. Find the speed of the train in $\text{km/hr}$.

When a train crosses a stationary pillar, the distance covered is equal to the length of the train.
$$\text{Distance}=335\text{m}$$

$$\text{Time}=18\text{seconds}$$

$$\text{Speed in m/s}=\frac{\text{Distance}}{\text{Time}}=\frac{335}{18}\text{m/s}$$

To convert the speed from $\text{m/s}$ to $\text{km/hr}$, multiply by $\frac{18}{5}$:

$$\text{Speed in km/hr}=\frac{335}{18}\times \frac{18}{5}=\frac{335}{5}=67\text{km/hr}$$