Question

The floor of a rectangular room has a perimeter 40m. If the cost of painting the
four walls at the rate of Rs. 25 per m2 is Rs. 1800. Find the height of the wall?

Answer 1

$$\begin{gathered} \mathrm{Perimeter}\mathrm{of}\mathrm{rectangular}\mathrm{floor}=2\left(\mathrm{l}+\mathrm{b}\right)=40\mathrm{m} \\ \mathrm{Area}\mathrm{of}\mathrm{four}\mathrm{walls}=\frac{\mathrm{Cost}\mathrm{of}\mathrm{painting}\mathrm{the}\mathrm{four}\mathrm{walls}}{\mathrm{Cost}\mathrm{of}\mathrm{painting}1{\mathrm{m}}^2} \\ =\frac{1800}{25}=72{\mathrm{m}}^2 \\ \mathrm{We}\mathrm{know}, \\ \mathrm{Area}\mathrm{of}\mathrm{four}\mathrm{walls}=2\left(\mathrm{l}+\mathrm{b}\right)\times \mathrm{h}=72 \\ 40\times \mathrm{h}=72 \\ \mathrm{h}=\frac{72}{40}=1.80\mathrm{m}. \\ \mathrm{Height}\mathrm{of}\mathrm{the}\mathrm{wall}\mathrm{is}1.80\mathrm{m}. \end{gathered}$$