The length, breadth and height of a room are 7.5 m, 4.5 m and 3.0 m respectively. There is a door of measure `2.0 m xx 1.0 m` and also 2 windows each of measure 1.2 m and 0.75 m. Find the cost of white washing its walls and roof at the rate of Rs. 1.20 per square metre.

Answer

To solve the problem, we will follow these steps:

### Step 1: Calculate the Area of the Four Walls
The area of the four walls of the room can be calculated using the formula:
\[ \text{Area of 4 walls} = 2 \times (l + b) \times h \]
where:
- \( l = 7.5 \, \text{m} \) (length)
- \( b = 4.5 \, \text{m} \) (breadth)
- \( h = 3.0 \, \text{m} \) (height)

Substituting the values:
\[ \text{Area of 4 walls} = 2 \times (7.5 + 4.5) \times 3 = 2 \times 12 \times 3 = 72 \, \text{m}^2 \]

### Step 2: Calculate the Area of the Roof
The area of the roof can be calculated using the formula:
\[ \text{Area of roof} = l \times b \]
Substituting the values:
\[ \text{Area of roof} = 7.5 \times 4.5 = 33.75 \, \text{m}^2 \]

### Step 3: Calculate the Area of the Door
The area of the door can be calculated using the formula:
\[ \text{Area of door} = \text{height} \times \text{width} = 2.0 \times 1.0 = 2.0 \, \text{m}^2 \]

### Step 4: Calculate the Area of the Windows
The area of one window can be calculated using the formula:
\[ \text{Area of one window} = 1.2 \times 0.75 = 0.9 \, \text{m}^2 \]
Since there are 2 windows:
\[ \text{Area of 2 windows} = 2 \times 0.9 = 1.8 \, \text{m}^2 \]

### Step 5: Calculate the Total Area to be Painted
The total area to be painted is given by:
\[ \text{Total area to be painted} = \text{Area of 4 walls} + \text{Area of roof} - \text{Area of door} - \text{Area of 2 windows} \]
Substituting the values:
\[ \text{Total area to be painted} = 72 + 33.75 - 2 - 1.8 = 101.95 \, \text{m}^2 \]

### Step 6: Calculate the Cost of White Washing
The cost of white washing is calculated using the formula:
\[ \text{Cost} = \text{Total area to be painted} \times \text{Rate per square meter} \]
Given the rate is Rs. 1.20 per square meter:
\[ \text{Cost} = 101.95 \times 1.20 = 122.34 \, \text{Rs.} \]

### Final Answer
The cost of white washing the walls and roof of the room is **Rs. 122.34**.

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