Question

How many cubic meters of earth must be dug out to make a well 28 m deep and 2.8 m in diameter? Also, find the cost of plastering its inner surface at Rs. 4.50 per sq.meter.

Answer 1

Radius of the well = ${\displaystyle \frac{2.8}{2}}$ = 1.4 m

Depth of the well = 28 m

Therefore, volume of earth dug out = πr²h

= ${\displaystyle \frac{22}{7}\times 1.4\times 1.4\times 28}$ 

= ${\displaystyle \frac{17248}{100}}$

= 172.48 m³

Area of curved surface = 2πrh

= ${\displaystyle 2\times \frac{22}{7}\times 1.4\times 28}$

= 246.40 m²

Cost of plastering the rate of Rs. 4.50 per sq m 

= Rs. 246.40 × 4.50

= Rs. 1108.8