How many cubic meters of earth must be dug out to sink a well which is 20 m deep and has a diameter of 7 meters? If the earth so dug out is spread over a rectangular plot 28 m by 11 m,what is the height of the platform so formed.
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The amount of earth to be removed is the volume of the cylinder of the well. It is cross section area time height. V= pi×r^2×h. r is 3 and h is 21
3.1416 × 3^2 × 21 = 593.8 cu meters
The plastering surface is the vertical surface of the cylindrical well. It is the circumference times the height. A= 2 × pi × r × h = 2 x 3.1416 × 3 × 21
A = 395.84 sq meter
At 20 rupees per sq meter the cost is 7917 rupee
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