How many cubic metres 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.metre.

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Solution

H=28m;
r=1.4m;

earth dug out=volume of cylinder= $\frac{22}{7} \times r \times r \times h$ ;
= $\frac{22}{7} \times 1.4 \times 1.4 \times 28$
= $172.48 m^{3}$
hence $172.48 m^{3}$ of earth is dug out

The curved surface area of the cylinder
= $2 \times \frac{22}{7} \times 1.4 \times 28$
= $246.4 m^{2}$

Cost of plastering= $4.50 \times 246.4$
=Rs 1108.8

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How many cubic metres 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.metre.

H=28m; r=1.4m; earth dug out=volume of cylinder= 227×r×r×h; = 227×1.4×1.4×28 =172.48m3 hence 172.48m3 of earth is dug out The curved surface area of the cylinder =2×227×1.4×28 =246.4m2 Cost of plastering= 4.50×246.4 =Rs 1108.8