The outer curved surface area of pencils having a diameter 7 mm and length 20 cm is coated with fine material. Find the amount spent on coating 1000 packets of pencils , each packet containing 10 pencils @ Rs 400 per sq. m.
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Diameter = 7mm = 0.7cm
Radius = 0.35cm
Length = 20cm
Pencil if a solid with a cylinder and a cone surmounted on it.
But as we need to find it's CSA,
CSA of pencil = CSA of cylinder
∴CSA of pencil = 2πrh
= 2*22/7*0.35*20
= 44*7/7
= 44cm²
1 packet = 10 pencils
1000packets = 10,000 pencils
W.K.T
44cm² = 0.004 m²
∴ The cost of coating the pencil is,
= 0.004 * 10,000
= ₹40
Therefore the cost is ₹40
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