document.write( "Question 145905: Alexander bell is selling answering machines. he sells two types a tape maching that sells for $8 and a disgital for $20. if he sells a ttoal of 30 answering machines and his total receipts were $492, how many of each type of answering machine did he sell \n" ); document.write( "
Algebra.Com's Answer #106488 by nerdybill(7384)\"\" \"About 
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Alexander bell is selling answering machines. he sells two types a tape maching that sells for $8 and a disgital for $20. if he sells a ttoal of 30 answering machines and his total receipts were $492, how many of each type of answering machine did he sell
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\n" ); document.write( "In algebra, assign variables to things you don't know. Then derive the necessary equations from the problem to solve it.
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\n" ); document.write( "Let t = number of tape machines sold
\n" ); document.write( "and d = number of digital machines sold
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\n" ); document.write( "Since there are two unknowns, we must derive two equations:
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\n" ); document.write( "Equation 1: \"he sells a total of 30 answering machines\" we get:
\n" ); document.write( "t + d = 30
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\n" ); document.write( "Equation 2: \"total receipts were $492\" and \"a tape maching that sells for $8 and a disgital for $20\" we get:
\n" ); document.write( "8t + 20d = 492
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\n" ); document.write( "Now we can solve:
\n" ); document.write( " t + d = 30
\n" ); document.write( "8t + 20d = 492
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\n" ); document.write( "Using the \"substitution\" method, solve equation 1 for t and plug it into equation 2:
\n" ); document.write( " t + d = 30
\n" ); document.write( " t = 30 - d
\n" ); document.write( "plugging it into equation 2:
\n" ); document.write( "8(30 - d) + 20d = 492
\n" ); document.write( "240 - 8d + 20d = 492
\n" ); document.write( "240 + 12d = 492
\n" ); document.write( "12d = 492-240
\n" ); document.write( "12d = 252
\n" ); document.write( "d = 21
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\n" ); document.write( "plug the above into equation 1 and solve for t:
\n" ); document.write( " t + d = 30
\n" ); document.write( " t + 21 = 30
\n" ); document.write( " t = 30 - 21
\n" ); document.write( " t = 9
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\n" ); document.write( "Sold 9 tape machines and
\n" ); document.write( "sold 21 digital machines\r
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