A flagstaff 17.5 m high caste a shadow of length 40.25 m. The height of the building, which casts a shadow of length 28.75 m under similar conditions will be ?

Let the height of the building be x metres
Lees lengthy shadow, Less is the height (Direct proportion)
$$\eqalign{ & \therefore 40.25:28.75::17.5:x \cr & \Leftrightarrow 40.25 \times x = 28.75 \times 17.5 \cr & \Leftrightarrow x = \frac{{\left( {28.75 \times 17.5} \right)}}{{40.25}} \cr & \Leftrightarrow x = 12.5 \cr} $$