Q8 of 20 Page 225

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.

Given, inner diameter of a circular well = 3.5 m i.e. r = 1.75m

Height = 10m


(i) curved surface area = 2πrh


= 2 × 3.14 × 1.75 × 10


= 109.9m2≃ 110cm2


(ii) cost of plastering = 40 × 110


= 4400


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