An open box is made of wood 3 cm thick. Its external length, breadth and height are 1.48 m, 1.16 m and 8.3 dm. Find the cost of painting the inner surface of Rs. 50per sq. metre.
Given,
Thickness of wood = 3cm
External length of box = 1.48 m = 148 cm
External breadth of box = 1.16 m = 116 cm
External height of box = 8.3 dm = 83 cm
So, inner dimensions of box = external dimension – thickness of wood
Inner length = 148- (2×3) = 142 cm
Inner breadth = 116 –(2×3) = 110 cm
Inner height = 83-3 = 80 cm
Hence , inner surface area of box = lateral surface area +area of roof
=2(l+b)h + l×b
= 2 (142+110)83 + 142×110 = 55940 cm2 = 5.5940 m2
∴ cost of painting at rate Rs.50 per m2 = 50×5.5940 = Rs. 279.70