Question

How many cubic metres of earth must be dug out to sink a well of 22.5m deep and diametre 7m ? Also,find the cost of plastering the inner curved surface at ₹3 per square metre.

Answer 1

volume of well=
$\pi {r}^{2} h$
$\frac{22}{7} \times \frac{7}{2} \times \frac{7}{2} \times 22.5 \\ = 866.25$
surface area of well=
$2\pi \: rh + \pi {r}^{2}$
$2 \times \frac{22}{7} \times \frac{7}{2} \times 22.5 \\ = 495$
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