Question

A classroom is 7 m long, 6 m broad and 3.5 m high. Doors and windows occupy an area of 17 m². What is the cost of white-washing the walls at the rate of Rs 1.50 per m².

Answer 1

$$\begin{gathered} \mathrm{Length}\mathrm{of}\mathrm{the}\mathrm{classroom}=7\mathrm{m} \\ \mathrm{Breadth}\mathrm{of}\mathrm{the}\mathrm{classroom}=6\mathrm{m} \\ \mathrm{Height}\mathrm{of}\mathrm{the}\mathrm{classroom}=3.5\mathrm{m} \\ \mathrm{Total}\mathrm{surface}\mathrm{area}\mathrm{of}\mathrm{the}\mathrm{classroom}\mathrm{to}\mathrm{be}\mathrm{whitewashed}=\mathrm{areas}\mathrm{of}\mathrm{the}4\mathrm{walls} \\ =2\times (\mathrm{breadth}\times \mathrm{height}+\mathrm{length}\times \mathrm{height}) \\ =2\times (6\times 3.5+7\times 3.5) \\ =2\times (21+24.5) \\ =91{\mathrm{m}}^2 \\ \mathrm{Also},\mathrm{the}\mathrm{doors}\mathrm{and}\mathrm{windows}\mathrm{occupy}17{\mathrm{m}}^2. \\ \mathrm{So},\mathrm{the}\mathrm{remaining}\mathrm{area}\mathrm{to}\mathrm{be}\mathrm{whitewashed}=91-17=74{\mathrm{m}}^2 \\ \mathrm{Given}\mathrm{that}\mathrm{the}\mathrm{cost}\mathrm{of}\mathrm{whitewashing}1{\mathrm{m}}^2\mathrm{of}\mathrm{wall}=\mathrm{Rs}1.50 \\ \therefore \mathrm{Total}\mathrm{cost}\mathrm{of}\mathrm{whitewashing}74{\mathrm{m}}^2\mathrm{of}\mathrm{area}=74\times 1.50=\mathrm{Rs}111 \end{gathered}$$