Find the cost of sinking a tubewell 280m deep having 3m

SOLUTION

Diameter of well = 3 m 
$\therefore$ Radius (r) = $\frac{3}{2}m$ and depth (h) = 280 m
(i) $\therefore$ Volume of earth dug out = $\pi r^{2}h$
= $\frac{22}{7}\times \frac{3}{2}\times \frac{3}{2}\times 280m^3=1980m^3$
Rate of sinking the well = Rs. 3.60 per $m^3$
$\therefore$ Total cost od sinking = Rs. 1980 $\times$ 3.60 per $m^3$
= Rs. 7,128
(ii) Inner curved surface area = $2\pi rh$
= $2\times \frac{22}{7}\times \frac{3}{2}\times 280m^2=2640m^2$
Rate of cementing =Rs. 2.50 per $m^2$ 
$\therefore$ Total cost of cementing = Rs 2.50 $\times$ 2640
= Rs. 6,600