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CBSE Class 9 Answered

A pillar has a spherical top of radius 20 cm. Find the cost of polishing the top of 35 such pillars at the rate of Rs 30 per m2.
Asked by Topperlearning User | 18 Oct, 2017, 03:23: PM
answered-by-expert Expert Answer

Given:         Radius (r) = 20 cm

Let S be the surface area of the spherical top.    

begin mathsize 12px style Surface space area space left parenthesis straight S right parenthesis space equals space 4 πr squared
equals space 4 cross times 22 over 7 cross times 20 cross times 20
equals space 35200 over 7 space cm squared end style

Surface area of 35 such balls= 35× begin mathsize 12px style 35200 over 7 space end style= 176000 cm2

Cost of polishing 1 m2 or 10000 cm=  Rs 30

Cost of polishing 176000 cm2=Rs (176000×begin mathsize 12px style 30 over 10000 end style) = Rs 528

Answered by | 18 Oct, 2017, 05:23: PM

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