Question

How many cubic m of soil must be dug to make a well 20 m deep and 2m in diameter . If the curved surface of the well is to be plastered at a rate of Rs. 50/meter square , find the cost of plastering?

Answer 1

Volume of soil to be taken out
=$\pi r^{2} h$
=$\frac{22}{7}* 1^{2} *20$
 =62.85 cubic m.   

Answer 2

volume of soil = volume of well
                     = pi*r²*h
                     = (22/7)1²*20
                      = 62.857 m³.
curved surface area of well = 2*pi*r*h
                                       = 2(22/7)*1*20
                                      = 125.714 m².
cost of plastering = 50*125.714 =  Rs. 6285.7