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 m^{2}.

`["Assume "pi=22/7]`

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#### Solution

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

Depth (*h*) of circular well = 10 m

Inner curved surface area = 2π*rh*

`=(2xx22/7xx1.75xx10)m^2`

= (44 × 0.25 × 10) m^{2}

= 110 m^{2}

Therefore, the inner curved surface area of the circular well is 110 m^{2}.

Cost of plastering 1 m^{2}_{ }area = Rs 40

Cost of plastering 110 m^{2}_{ }area = Rs (110 × 40)

= Rs 4400

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

Concept: Surface Area of Cylinder

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