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CBSE Class 9 Answered

A spherical metal ball has radius 4.2 cm. Find the cost of polishing 10 such balls at the rate of Rs 5 per 100 cm2.
Asked by Topperlearning User | 18 Oct, 2017, 03:15: PM
answered-by-expert Expert Answer

Given:         Radius (r) = 4.2 cm

Let S be the surface area of the sphere.        

 

begin mathsize 12px style Surface space area space left parenthesis straight S right parenthesis space equals space 4 πr squared equals 4 cross times 22 over 7 cross times 4.2 cross times 4.2 equals 221.76 space cm squared end style

Surface area of 10 such balls = 10×221.76 cm2 = 2217.6 cm2

Cost of polishing 100 cm2 = Rs 5

Cost of polishing 2217.6 cm2 = Rs (2217.6×) = Rs 110.88

Answered by | 18 Oct, 2017, 05:15: PM

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