A rectangular room has dimensions 10 m (length), 7 m (breadth), and 5 m (height). There are 2 identical doors and 3 windows in the room. Each door is 1 m * 3 m. Among the windows, 1 window is 2 m * 1.5 m and the other 2 windows are 1 m * 1.5 m each. Find the total cost of painting only the four walls (not the floor or ceiling) at the rate of ₹3 per sq m, after excluding the areas of the doors and windows from the paintable wall area.

Introduction / Context:
This question tests the standard “area of four walls” concept used in mensuration, along with the practical adjustment of subtracting openings like doors and windows before calculating painting cost. The key is to compute the lateral surface area of a room (four walls only), then subtract the total area covered by doors and windows, and finally multiply by the painting rate per square metre.

Given Data / Assumptions:

• Length l = 10 m, breadth b = 7 m, height h = 5 m
• 2 doors, each 1 m * 3 m
• 1 window of 2 m * 1.5 m
• 2 windows of 1 m * 1.5 m each
• Painting rate = ₹3 per sq m
• Paint only four walls (exclude floor and ceiling)

Concept / Approach:
Area of four walls = 2 * (l + b) * h. Subtract openings area. Cost = (net paintable area) * rate.

Step-by-Step Solution:

Verification / Alternative check:
The paintable area must be slightly less than 170 sq m because openings are removed. Removing 12 sq m is reasonable for 2 doors and 3 windows, so 158 sq m is consistent. Multiplying by ₹3 gives ₹474, which fits the expected scale.

Why Other Options Are Wrong:

Common Pitfalls:
Common errors include using 2 * l * b (floor area) instead of wall area, forgetting to multiply by height, or subtracting only one door/window instead of all. Another mistake is including the ceiling in painting when the question asks only walls.

Final Answer:
₹474