document.write( "Question 1010672: you have $13.80 in quarters and dimes. if you have 84 coins, how many are dimes?
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Algebra.Com's Answer #626129 by Edwin McCravy(20056) $\"\"$ $\"About$

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document.write( "Let the number of quarters be x\r\n" );
document.write( "Let the number of dimes be y\r\n" );
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document.write( "                      Value      Value\r\n" );
document.write( "Type       Number       of         of\r\n" );
document.write( " of          of        EACH       ALL\r\n" );
document.write( "coin        coins      coin      coins\r\n" );
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document.write( "quarters     x        $0.25     $0.25x\r\n" );
document.write( "dimes        y        $0.10     $0.10y\r\n" );
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document.write( "TOTALS      84       -----      $13.80\r\n" );
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document.write( " The first equation comes from the second column.\r\n" );
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document.write( "  \r\n" );
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document.write( "                 x + y = 84\r\n" );
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document.write( " The second equation comes from the last column.\r\n" );
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document.write( "           0.25x + 0.10y = 13.80\r\n" );
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document.write( "Get rid of decimals by multiplying every term by 100:\r\n" );
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document.write( "               25x + 10y = 1380\r\n" );
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document.write( " So we have the system of equations:\r\n" );
document.write( "           .\r\n" );
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document.write( "We solve by substitution.  Solve the first equation for y:\r\n" );
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document.write( "           x + y = 84\r\n" );
document.write( "               y = 84 - x\r\n" );
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document.write( "Substitute (84 - x) for y in 25x + 10y = 1380\r\n" );
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document.write( "   25x + 10(84 - x) = 1380\r\n" );
document.write( "    25x + 840 - 10x = 1380\r\n" );
document.write( "          15x + 840 = 1380\r\n" );
document.write( "                15x = 540\r\n" );
document.write( "                  x = 36 = the number of quarters.\r\n" );
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document.write( "Substitute in y = 84 - x\r\n" );
document.write( "              y = 84 - (36\r\n" );
document.write( "              y = 48 dimes.\r\n" );
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document.write( "Checking:  36 quarters is $9.00 and 48 dimes is $4.80\r\n" );
document.write( "            That's 84 coins.\r\n" );
document.write( "            And indeed $9.00 + $4.80 = $13.80\r\n" );
document.write( "Edwin

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