**Question:**

The walls and ceiling of a room are to be plastered. The length, breadth and height of the room are 4.5 m, 3 m and 350 cm, respectively. Find the cost of plastering at the rate of Rs 8 per square metre.

**Solution:**

Length of a room $=4.5 \mathrm{~m}$

Breadth $=3 \mathrm{~m}$

Height $=350 \mathrm{~cm}$

$=\frac{350}{100} \mathrm{~m} \quad(\because 1 \mathrm{~m}=100 \mathrm{~cm})$

$=3.5 \mathrm{~m}$

Since only the walls and the ceiling of the room are to be plastered, we have:

So, total area to be plastered $=$ area of the ceiling $+$ area of the walls

$=($ length $\times$ breadth $)+2 \times($ length $\times$ height $+$ breadth $\times$ height $)$

$=(4.5 \times 3)+2 \times(4.5 \times 3.5+3 \times 3.5)$

$=13.5+2 \times(15.75+10.5)$

$=13.5+2 \times(26.25)$

$=66 \mathrm{~m}^{2}$

Again, cost of plastering an area of $1 \mathrm{~m}^{2}=$ Rs 8

$\therefore$ Total cost of plastering an area of $66 \mathrm{~m}^{2}=66 \times 8=$ Rs 528