# Ex 11.3, 8 - Chapter 11 Class 7 Perimeter and Area

Last updated at Dec. 12, 2018 by Teachoo

Ex 11.3

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Ex 11.3, 8 You are here

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Last updated at Dec. 12, 2018 by Teachoo

Ex 11.3, 8 Find the cost of polishing a circular table-top of diameter 1.6 m, if the rate of polishing is Rs 15/m2. (Take π = 3.14) Here, Area to be polished = Area of circular table top Diameter = 1.6 m Radius = r = 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟/2 = 1.6/2 = 16/(2 × 10) = 8/10 m Area of table top = 𝜋r2 = 3.14 × (8/10)^2 = 314/100 × 8/10 × 8/10 = (314 × 64)/10000 = 20096/10000 = 2.0096 m2 Now, Cost of polishing 1 m2 area = Rs 15 Cost of polishing 2.0096 m2 area = Rs 15 × 2.0096 = Rs 15 × 20096/10000 = Rs 3 × 20096/2000 = Rs 3 × 10048/1000 = Rs 30144/1000 = Rs 30.144 = Rs 30.14 (approx.) ∴ It will cost Rs 30.14 (approx.) to polish the table top