How many cubic metres of earth msut be dugout to sink a well 21 m deep and 6 m diameter? Find the cost of plastering the inner surface of the well at Rs. 9.50 per m2.
Given,
Depth of well = 21m
Diameter of well = 6m
So, radius of well = 
Volume of earth that can be dug out = πr2h = 
Inner curved surface area of cylindrical well = 2πrh = 
Cost of plastering 1 m2 area = Rs. 9.50
∴cost of plastering 396 m2 area = 396×9.50 = Rs. 3762
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