Find the cost of plastering the inner surface of a well at Rs 9.50 per

Question:

Find the cost of plastering the inner surface of a well at Rs 9.50 per m2, if it is 21 m deep and diameter of its top is 6 m.

Solution:

Given :

Height, $h=21 \mathrm{~m}$

Diameter, $d=6 \mathrm{~m}$

Radius, $r=3 \mathrm{~m}

Area of the inner surface of the well, $S=2 \pi r h$

$=2 \pi \times 3 \times 21 \mathrm{~m}^{2}$

$=2 \times \frac{22}{7} \times 3 \times 21 \mathrm{~m}^{2}$

$=396 \mathrm{~m}^{2}$

According to question, the cost per $\mathrm{m}^{2}$ is Rs $9.50$.

$\therefore$ Inner surface cost is Rs $396 \times 9.50=$ Rs 3762

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