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Question
How many cubic meters of earth must be dug out to sink a well 42m deep and 14m in diameter? Find the cost of plastering the inside walls of the well at Rs.15per m2.
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Solution
Depth or height (h) of cylindrical well = 42m
Diameter = 14m
∴ Radius (r) = 7m
Volume of the well
= π x r2 x h
= `(22)/(7) xx 7^2 xx 42`
= 6468m3
Curved surface area of walls
= 2 x π x r x h
= `2 xx (22)/(7) xx 7 xx 42`
= 1848m2
Cost of plastering 1m2 area of the well = Rs.15
∴ Cost of plastering 1848m2 area of wall
= Rs.15 x 1848
= Rs.27,720.
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