The dimensions of a room are 12.5 metres by 9 metres by 7 metres. There are 2 doors and 4 windows in the room; each door measures 2.5 metres by 1.2 metres and each window 1.5 metres by 1 metre. Find the cost of painting the walls at Rs. 3.50 per square metre.

The dimensions of a room are 12.5 metres by 9 metres by 7 metres. There are 2 doors and 4 windows in the room; each door measures 2.5 metres by 1.2 metres and each window 1.5 metres by 1 metre. Find the cost of painting the walls at Rs. 3.50 per square metre. Correct Answer Rs. 1011.50

Area of 4 walls :
$$\eqalign{ & = 2\left( {l + b} \right) \times h \cr & = \left{m^2} \cr & = 301\,{m^2} \cr} $$
Area of 2 doors and 4 windows :
$$\eqalign{ & = \left{m^2} \cr & = 12\,{m^2} \cr} $$
∴ Area to be painted :
$$\eqalign{ & = \left( {301 - 12} \right){m^2} \cr & = 289\,{m^2} \cr} $$
Cost of painting :
$$\eqalign{ & = {\text{Rs}}{\text{.}}\left( {289 \times 3.50} \right) \cr & = {\text{Rs}}{\text{. }}1011.50 \cr} $$