The dimension of a room is 10 m ×8 m ×4 m. There are 3 windows and 1 door of dimensions 1.5 m ×0.8 m and 2 m ×1.6 m respectively. Find the cost of whitewashing the rooms and the ceiling from inside at a rate of Rs 12.50 per m².

Given that the length (l), breadth (b), and height (h) of the cuboidal-shaped room are 10 m, 8 m, and 4 m respectively.

Therefore, area of 4 walls and ceiling from inside = 2h(l+b) + lb 

= 2 ×4 m ×(10 m + 8 m) + 10 m ×8 m

= (144 + 80) m²

= 224 m²

Area of 3 windows = 3 ×1.5 m ×0.8 m = 3.6 m²

Area of 1 door = 2 m ×1.6 m = 3.2 m

Now, area of 4 walls and ceiling, which does not include the 3 windows and the door = [224 − (3.6 + 3.2)] m²= 217.2 m²

Therefore, cost of whitewashing = Rs (12.50 ×217.2) = Rs 2715