Question

A well with 7m diameter is 10m deep. find the cost of plastering its inner curved surface area at the rate of 30 per meter square

Answer 1

R = 7/2 m
H = 10 m

Csa = 2 pi rh
= 2 * 22/7 * 7/2 * 10
= 220 sq m

Cost = 220 * 30
. . . . = Rs. 660

Answer 2

The cost of plastering its inner curved surface area at the rate of 30 per meter square is Rs. 6600.

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Let's understand a few concepts:

To calculate the cost of plastering the inner curved surface area of the well which is cylindrical in shape we have to first find the curved surface area of the cylindrical well by using the below-mentioned formula and then multiply the rate of 30 per meter square:

$\boxed{\bold{Curved \:surface\:area \:of \:a \:cylinder = 2\pi rh}}$

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Let's solve the given problem:

The inner diameter of the well (d) = 7 m

So, the inner radius of the well (r) = $\frac{7}{2} \:m$

The inner depth of the well = Height of the cylinder (h) = 10 m

Therefore,

The inner curved surface area of the well is,

= C.S.A. of a cylinder

= $2\pi rh$

= $2\times \frac{22}{7} \times \frac{7}{2} \times 10$

= $220 \:m^2$

Now,

If the cost of plastering 1 m² of the well = Rs. 30

Then,

The cost of plastering the 220 m² well is,

= Rs. 30/m² × 220 m²

= Rs. 6600

Thus, the cost of plastering the inner curved surface area of the well at the rate of 30 per meter square is Rs. 6600.

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