Question

The dimensions of a room are (9 m × 8 m × 6.5 m). It has one door of dimensions (2 m × 1.5 m) and two windows, each of dimensions (1.5 m × 1 m). Find the cost of whitewashing the walls at Rs 6.40 per square metre.

Answer 1

We need to white wash the four walls of the room
Here, l = 9 m; b = 8 m; h = 6.5 m
Area of the four walls = $\left[2\left(l+b\right)\times h\right]$
$$\begin{gathered} =\left[2\left(9+8\right)\times 6.5\right]{\mathrm{m}}^2 \\ =2\times 17\times 6.5{\mathrm{m}}^2 \\ =221{\mathrm{m}}^2 \end{gathered}$$
Now, the door and the windows are not to be white washed.
Area of the door = $l\times b=2\times 1.5=3{\mathrm{m}}^2$
Area of a window = $l\times b=1.5\times 1=1.5{\mathrm{m}}^2$

Area to be white washed = area of four walls − (area of door + area of two windows)
= 221 − (3 + 2 $\times$ 1.5)
= 221 − 6 = 215 m²
Cost of whitewashing = Rs 6.40/m²
∴ Cost of whitewashing 215 m² = Rs 6.40 $\times$ 215 = Rs 1376