<PRE><B>Question 113457</B>
Jim wants to buy cement to anchor two posts for a swing he is building. He has dug 2 round holes that 12 inches in diameter and 40 inches deep. He wants to fill each with concrete around a rectangular supporting beam that is 3.5 inches by 5.5 inches. Each 80-pound bag of concrete mixes with water to make 0.6 cubic fee of concrete. How many bags of concrete must he buy for the job? 
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Volume of the post: 3.5*5.5*40 = 770 cu. in.
Volume of the holes: 2*(pi)6^2*40 = 9047.786842 cu. in
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Volume he needs to fill with concrete:
9047.786842-770 = 8277.786842 cu. in
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1 cu. ft of of concrete = 12*12*12 = 1728 cu. in.
0.6 cu. ft. = 0.6*1728 = 1036.8 cu. in.
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# of bags = 8277.786842/1036.8 = 7.98 bags
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He needs to buy 8 bags.
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Cheers,
Stan H.</PRE>