If a 7-storey building has a 28 m long shadow, the number of storeys of the building whose shadow is 48 m long is:

​Height of the 7-storey building = unknown,

Shadow length of 7-storey building = 28 m

Shadow length of the unknown building = 48 m

The shadow length is proportional to the height of the building.

Let the number of storeys of the building with a 48 m shadow be "x". Since the shadow is proportional to the building height.

​$$\begin{aligned}&\frac{7}{x} = \frac{28}{48}\\ ​&7 \times 48 = x \times 28\\&x = \frac{336}{28} = 12\end{aligned}$$​​

Hence, the building with a 48 m shadow has 12 storeys.

By ratio method :

​$$\text{Number of storeys} \propto \text{Shadow length}$$​​

​$$\frac{7}{x} = \frac{28}{48} ​$$​​

This directly gives x = 12.

unitary method: