"Question 2 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 .
Class 9 - Math - Surface Areas and Volumes Page 213"
Answers
breadth of the room = 4m
height of the room = 3m
Area of four walls including the ceiling = 2(l+b)×h + (l×b)
= 2(5+4)×3 + (5×4) m2
= (54 + 20) m2
= 74 m2 Cost of white washing = ₹7.50 per m2
Total cost = ₹ (74×7.50) = ₹ 555
Lateral surface area of a cuboid:
If out of the 6 faces of a cuboid we do not include the bottom and top faces then the area of remaining four faces is called the lateral surface area of cuboid .
Area of four walls of a room= lateral surface area of a cuboid= 2(l+b)h
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Given , Dimensions of room are
length of the room(l) = 5m
breadth of the room(b) = 4m
height of the room(h) = 3m
Required area for white washing=Area of four walls + Area of ceiling = 2(l+b)×h + (l×b)
= 2(5+4)×3 + (5×4)
= 2×9×3 + 20
=(54 + 20)
= 74 m²
Cost of white washing = ₹7.50 per m²
Total cost of white washing= ₹ (74×7.50) = ₹ 555
Hence, the cost of white washing the walls of the room and the ceiling= ₹555.
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Hope this will help you....