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CBSE Class 9 Answered

The slant height and altitude of a conical tomb are 15 m and 12 m respectively. Find the cost of white-washing its curved surface at the rate of Rs. 70 per m2.
Asked by Topperlearning User | 17 Oct, 2017, 09:56: AM
answered-by-expert Expert Answer

Altitude (h) = 12 m, slant height (l) =15 m. Let radius = r

 

begin mathsize 12px style l squared italic space equals space straight r squared space plus space straight h squared straight r space italic space italic space equals space square root of l squared space minus space straight h squared end root straight r space equals space square root of 15 squared space minus space 12 squared end root straight r space equals space 9 space straight m end style

Thus, r = 9 m. 

begin mathsize 12px style Curved space surface space area space equals space πr l equals space 22 over 7 cross times 9 cross times 15 equals space 2970 over 7 space straight m squared end style

Cost of white washing 1 m2 of canvas = Rs. 70

Therefore, cost of whitewashing begin mathsize 12px style 2970 over 7 space straight m squared end style = Rs. (begin mathsize 12px style 2970 over 7 end style×70)

                                                            = Rs. 29700

Answered by | 17 Oct, 2017, 11:56: AM

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