document.write( "Question 615961: please help
\n" ); document.write( "The cost of six CDs and four DVDs is $77.80; and the cost of fourteen DVDs and eleven CDs is $192.25. How much do a CD and a DVD cost? \n" ); document.write( "
Algebra.Com's Answer #387405 by Theo(13342)\"\" \"About 
You can put this solution on YOUR website!
c = number of cd's that were bought.
\n" ); document.write( "d = the number of dvds that were bought.
\n" ); document.write( "6c + 4d = 77.80
\n" ); document.write( "11c + 14d = 192.25
\n" ); document.write( "use one of the equations to solve for d in terms of c.
\n" ); document.write( "then use that value for d in the other equation.
\n" ); document.write( "from the first equation, you get:
\n" ); document.write( "6c + 4d = 77.80
\n" ); document.write( "subtract 6c from both sides of the equation to get:
\n" ); document.write( "4d = 77.80 - 6c
\n" ); document.write( "divide both sides of the equation by 4 to get:
\n" ); document.write( "d = (77.80 - 6c) / 4
\n" ); document.write( "substitute this equation for d in the other equation to get:
\n" ); document.write( "11c + 14d = 192.25 becomes:
\n" ); document.write( "11c + 14*((77.80-6c)/4) = 192.25
\n" ); document.write( "simplify by removing parentheses to get:
\n" ); document.write( "11c + (1089.2 - 84c)/4 = 192.25
\n" ); document.write( "multiply both sides of the equation by 4 to get:
\n" ); document.write( "44c + 1089.2 - 84c = 769
\n" ); document.write( "subtract 1089.2 from both sides of the equation to get:
\n" ); document.write( "44c - 84c = 769 - 1089.2
\n" ); document.write( "simplify to get:
\n" ); document.write( "-40c = -320.2
\n" ); document.write( "divide both sides of the equation by -40 to get:
\n" ); document.write( "c = 8.005
\n" ); document.write( "take the first original equation and replace c with 8.005 and solve for d.
\n" ); document.write( "the first original equation is:
\n" ); document.write( "6c + 4d = 77.80
\n" ); document.write( "replace c with 8.005 to get:
\n" ); document.write( "6*8.005 + 4d = 77.80
\n" ); document.write( "simplify to get:
\n" ); document.write( "48.03 + 4d = 77.80
\n" ); document.write( "subtract 48.03 from both sides of the equation to get:
\n" ); document.write( "4d = 77.80 - 48.03
\n" ); document.write( "simplify to get:
\n" ); document.write( "4d = 29.77
\n" ); document.write( "divide both sides of the equation by 4 to get:
\n" ); document.write( "d = 7.4425
\n" ); document.write( "you have:
\n" ); document.write( "c = 8.005
\n" ); document.write( "d = 7.4425
\n" ); document.write( "substitute these values for c and d in the second original equation.
\n" ); document.write( "11c + 14d = 192.25 becomes:
\n" ); document.write( "11*8.005 + 14*74425 = 192.25
\n" ); document.write( "simplify to get:
\n" ); document.write( "88.055 + 104.195 = 192.25 which becomes:
\n" ); document.write( "192.25 = 192.25 confirming the values for c and d are correct.\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );