The inner diameter of a circular well is 3.5 m. It is 10 m deep.

Question:

The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find the cost of plastering its inner curved surface at Rs 4 per square metre.

Solution:

Given:

Inner diameter of the circular well $=3.5 \mathrm{~m}$

$\therefore$ Inner radius of the circular well, $r=1.75 \mathrm{~m}$

Depth of the circular well, $h=10 \mathrm{~m}$

Inner curved surface area, $S=2 \pi r h$

$\mathrm{S}=2 \pi \times 1.75 \times 10 \mathrm{~m}^{2}=2 \times \frac{22}{7} \times 1.75 \times 10 \mathrm{~m}^{2}$

$=110 \mathrm{~m}^{2}$

Cost of plastering $1 \mathrm{~m}^{2}$ area $=\mathrm{Rs} 4$

Cost of plastering $110 \mathrm{~m}^{2}$ area $=\mathrm{Rs}(110 \times 4)=\mathrm{Rs} 440$

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