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

\[\text { Length of a room = 4 . 5 m } \]

\[\text { Breadth = 3 m } \]

\[\text { Height = 350 cm }\]

\[ = \frac{350}{100}m ( \because 1 m = 100 cm )\]

\[ = 3 . 5 m\]

\[\text { Since only the walls and the ceiling of the room are to be plastered, we have: }\]

\[\text { So, total area to be plastered = area of the ceiling + area of the walls }\]

\[ =\text { (length }\times \text { breadth) } + 2 \times \text { (length }\times \text { height + breadth } \times \text { height) }\]

\[ = (4 . 5 \times 3) + 2 \times (4 . 5 \times 3 . 5 + 3 \times 3 . 5)\]

\[ = 13 . 5 + 2 \times (15 . 75 + 10 . 5)\]

\[ = 13 . 5 + 2 \times (26 . 25)\]

\[ = 66 m^2 \]

\[\text { Again, cost of plastering an area of 1 }m^2 = \text { Rs } 8 \]

\[ \therefore \text { Total cost of plastering an area of 66 } m^2 = 66 \times 8 = \text { Rs }528\]