document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1207766>Question 1207766</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A 20-pound bag of Economy brand cement mix contains 25% cement and 75% sand. How much pure cement must be added to produce a cement mix that is 40% cement?\r<BR>\n" );
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document.write( "I came up with this equation:\r<BR>\n" );
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document.write( "0.25x + 0.75x = 0.40(2x)\r<BR>\n" );
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document.write( "You say? </SPAN>\n" );
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document.write( "The 20-pound bag is 25% (=1/4) cement and 75% (=3/4) sand, so it contains 5 pounds of cement and 15 pounds of sand.<br><BR>\n" );
document.write( "Let x be the number of pounds of cement you add.  Then the number of pounds of cement is 5+x, and the total weight is 20+x.<br><BR>\n" );
document.write( "You want the cement to be 40% of the total weight:<br><BR>\n" );
document.write( "(5+x) = 0.40(20+x)<br><BR>\n" );
document.write( "5+x = 8+0.40x<BR>\n" );
document.write( "x-0.40x = 8-5<BR>\n" );
document.write( "0.60x = 3<BR>\n" );
document.write( "x = 3/0.60 = 5<br><BR>\n" );
document.write( "ANSWER: 5 pounds<br><BR>\n" );
document.write( "CHECK: the total weight is now 20+5 = 25 pounds; the number of pounds of cement is 5+5 = 10; 10/25 = 0.40<br><BR>\n" );
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