The length, breadth and height of a room are 5 m, 4 m and 3 m respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of Rs. 7.50 per \({m}^2\).

Given :
Length (l) of room = 5 m
Breadth (b) of room = 4 m
Height (h) of room = 3 m

It can be observed that four walls and the ceiling of the room are to be white- washed. The floor of the room is not to be white-washed.

So, we get,

Area to be white-washed
= Area of walls + Area of ceiling of room
= 2lh + 2bh + lb
= [2 x 5 x 3 + 2 x 4 x 3 + 5 x 4] \({m}^2\)
= [30 + 24 + 20] \({m}^2\)
= 74 \({m}^2\).

Now, we have,
Cost of white-washing per \({m}^2\) area = Rs. 7.50
Cost of white-washing 74 \({m}^2\) area = Rs. (74 x 7.50) = Rs. 555

Therefore, the cost of white washing the walls of the room and the ceiling is Rs. 555.