Question

The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find the cost of plastering its inner curved surface at Rs 4 per square metre.

Answer 1

$$\begin{gathered} \mathrm{Given}: \\ \mathrm{Inner}\mathrm{diameter}\mathrm{of}\mathrm{the}\mathrm{circular}\mathrm{well}=3.5\mathrm{m} \\ \therefore \mathrm{Inner}\mathrm{radius}\mathrm{of}\mathrm{the}\mathrm{circular}\mathrm{well},r=1.75\mathrm{m} \\ \mathrm{Depth}\mathrm{of}\mathrm{the}\mathrm{circular}\mathrm{well},h=10\mathrm{m} \\ \mathrm{Inner}\mathrm{curved}\mathrm{surface}\mathrm{area},S=2\mathrm{\pi }rh \\ \mathrm{S}=2\mathrm{\pi }\times 1.75\times 10{\mathrm{m}}^2=2\times \frac{22}{7}\times 1.75\times 10{\mathrm{m}}^2 \\ =110{\mathrm{m}}^2 \\ \mathrm{Cost}\mathrm{of}\mathrm{plastering}1{\mathrm{m}}^2\mathrm{area}=\mathrm{Rs}4 \\ \mathrm{Cost}\mathrm{of}\mathrm{plastering}110{\mathrm{m}}^2\mathrm{area}=\mathrm{Rs}\left(110\times 4\right)=\mathrm{Rs}440 \end{gathered}$$