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The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find 

(i) its inner curved surface area, 

(ii) the cost of plastering this curved surface at the rate of Rs 40 per m2

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2 Answers

Here, r = 3. 5/ 2 m , h = 10 m 

(i) Inner curved surface area of the well 

= 2πrh = 2 × 22/ 7 × 3. 5 /2  × 10m2 

= 22 × 5 m2 = 110 m2 Ans. 

(ii) Cost of plastering 1 m2 = Rs 40 

∴ Cost of plastering the curved surface area of the well 

= Rs 110 × 40 = Rs 4400 Ans

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Inner radius (r) of circular well = (3.5/2)m = 1.75m

Depth (h) of circular well = 10 m

Inner curved surface area = 2πrh

= (2 x 22/7 x 1.75 x 10) m2

= (44 x 0.25 x 10) m2

= 110 m2

Therefore, the inner curved surface area of the circular well is 110 m2.

Cost of plastering 1 m2 area = Rs 40

Cost of plastering 100 m2 area = Rs (110 × 40) = Rs 4400

Therefore, the cost of plastering the CSA of this well is Rs 4400.

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