Question : A cuboidal room's internal measures are a length of 12 m, a breadth of 8 m, and a height of 10 m. The total cost (in INR ) of whitewashing all four walls of the room and also the ceiling of the room, if the cost of whitewashing is INR 25 per m2 is:
Option 1: 12,400
Option 2: 12,000
Option 3: 18,000
Option 4: 13,600
Correct Answer: 12,400
Solution :
The lateral surface area of the room = 2 × h × (l + b), where l = length, b = breadth, and h = height.
According to the question
Lateral surface area = Area of walls
= 2 × 10 × (12 + 8) = 20 × 20 = 400 m
2
and, Area of ceiling = 12 × 8 = 96 m
2
So, total cost of whitewashing = 25 × (400 + 96) = INR 12,400
Hence, the correct answer is 12,400.
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