document.write( "Question 242723: during one month, a homeowner used 400 units of electricity and 150 units of gas for a total cost of $76.50. the next month, 450 units of electricity and 100 units of gas were used for a total cost of $78.50. find the cost per unit of electricity. \n" ); document.write( "
Algebra.Com's Answer #177677 by blwinbbbles(106)\"\" \"About 
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so write down what we know:\r
\n" ); document.write( "\n" ); document.write( "e = electric g = gas\r
\n" ); document.write( "\n" ); document.write( "We know that in one month: (1)400e + 150g = $76.50
\n" ); document.write( "and in the next month: (2)450e + 100g = $78.50\r
\n" ); document.write( "\n" ); document.write( "So we need to use elimination to solve this problem.\r
\n" ); document.write( "\n" ); document.write( "Let's eliminate the g..to do that we need to make the units of g's exact opposites, so that when we add the equations we will get zero for the g.\r
\n" ); document.write( "\n" ); document.write( "The easiest way to do that is multiple equation 2 by -1.5
\n" ); document.write( "this will give us:\r
\n" ); document.write( "\n" ); document.write( "-675e - 150g = -117.75
\n" ); document.write( "now add this equation to equation 1\r
\n" ); document.write( "\n" ); document.write( " 400e + 150g = $76.50
\n" ); document.write( "-675e - 150g = -$117.50\r
\n" ); document.write( "\n" ); document.write( "the answer is -275e = -$41.25\r
\n" ); document.write( "\n" ); document.write( "divide both sides by -275 and you get e = $0.15\r
\n" ); document.write( "\n" ); document.write( "So one unit of electricity is $0.15
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