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Find the cost of plastering the inner surface of a well at Rs.9.50 per $m 2$ , if it is 21 m deep and diameter of its top is 6 m.

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Rs.3276

Rs.3726

Rs.3672

Rs.3762

answer is D.

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Detailed Solution

It is given a well of depth 21 m and diameter of its top is 6 m and the cost of plastering the inner surface of well is Rs.9.50 per

m 2

.
Let the radius of the cylinder be `r’ cm.

R a d i u s = d i a m e t e r 2

Radius of cylinder

⇒

Radius=3m
Curved surface area of cylinder is

2 π r h

C . S . A . = 2 π r h ⇒ C . S . A . = 2 × 227 × 3 × 21

⇒ C . S . A . = 2 × 22 × 3 × 3

Cost of plastering the inner surface at the rate of Rs.9.50 per sq. m

Cost=396×9 .50 ⇒ Cost=Rs .3762

The cost of plastering the inner surface is Rs.3762.
Hence option (4) is correct.

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