The length of a room is 5m, breadth is 3.5m and height is 4m. Find the total expenditure of whitewashing on the four walls and roof at the rate of 15 per square meter. (Ans: correctly up to 1 decimal place)

# The length of a room is 5m, breadth is 3.5m and height is 4m. Find the total expenditure of whitewashing on the four walls and roof at the rate of 15 per square meter. (Ans: correctly up to 1 decimal place)

1. A
Rs.1282.5
2. B
Rs.1280.5
3. C
Rs.1272.5
4. D
Rs.1143.5

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### Solution:

Write the dimensions of room
Since, length
Since, height
Now we write the formula of surface area of walls and floor of the room

Let the total surface area of the cuboidal room be .
Then we can write the formula of total surface area of room as
Since we have to find the surface area of four walls and roof of the room, we subtract the area of the floor. Let the surface area of four walls and roof of the room be denoted by .
Area of floor of the room⇒Surface area of four walls and roof of the room
Calculate the value in RHS

Calculate the area to be white washed
Substitute the values of  in equation (1)
⇒Area of walls to be white washed ⇒Area of walls to be white washed
Add the terms within the bracket
⇒Area of walls to be white washed
Now we calculate the cost of white washing the total area obtained
Use a unitary method to calculate the cost of white washing the walls and roof by multiplying the total surface area of walls and walls by cost of white washing per unit square meter.
Cost of white washing 1 sq.m of room = Rs15
⇒Cost of white washing 85.5 sq.m of room⇒Cost of white washing 85.5 sq.m of room ∴ Cost of white washing four walls and roof of the room is.
Hence, option 1 is the correct Ans:.

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