document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=985202>Question 985202</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Four CDs and three DVDs cost €108, while one DVD and three CDs cost €56.<BR>\n" );
document.write( "Find the cost of a CD and the cost of a DVD.<BR>\n" );
document.write( "Let c = cost of a CD<BR>\n" );
document.write( "d = cost of a DVD. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #606024 by </B><A HREF=/tutors/aboutme.mpl?userid=srinivas.g><B>srinivas.g(540)</B></A><img src=\"/images/stars/stars-10.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=srinivas.g><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=srinivas.g><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=606024\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> et c = cost of a CD<BR>\n" );
document.write( "d = cost of a DVD<BR>\n" );
document.write( "Four CDs and three DVDs cost €108<BR>\n" );
document.write( " 4c+3d =108........(1)<BR>\n" );
document.write( "one DVD and three CDs cost €56<BR>\n" );
document.write( "3c+d=56...........(2)<TABLE  BORDER=1>\n" );
document.write( "\n" );
document.write( " <TR><TD  ALIGN=MIDDLE>Solved by <A  rel=nofollow HREF=http://wiki.algebra.com/index.php/Tutoring_-_pluggable_solvers>pluggable</A> solver: <A  rel=nofollow HREF=linear_substitution.solver>SOLVE linear system by SUBSTITUTION</A></TD></TR>\n" );
document.write( "<TR><TD  ALIGN=LEFT>Solve:<BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+system%28+%0D%0A++++4%5Cc+%2B+3%5Cd+=+108%2C%0D%0A++++3%5Cc+%2B+1%5Cd+=+56+%29%0D%0A++ ALIGN=MIDDLE  ALT=\"+system%28+%0D%0A++++4%5Cc+%2B+3%5Cd+=+108%2C%0D%0A++++3%5Cc+%2B+1%5Cd+=+56+%29%0D%0A++\"   DISABLED_style= \"max-width:90%; height:auto;\" >We'll use substitution. After moving 3*d to the right, we get:<BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=4%2Ac+=+108+-+3%2Ad ALIGN=MIDDLE  ALT=\"4%2Ac+=+108+-+3%2Ad\"   DISABLED_style= \"max-width:90%; height:auto;\" >, or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=c+=+108%2F4+-+3%2Ad%2F4 ALIGN=MIDDLE  ALT=\"c+=+108%2F4+-+3%2Ad%2F4\"   DISABLED_style= \"max-width:90%; height:auto;\" >. Substitute that<BR>\n" );
document.write( "  into another equation:<BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=3%2A%28108%2F4+-+3%2Ad%2F4%29+%2B+1%5Cd+=+56 ALIGN=MIDDLE  ALT=\"3%2A%28108%2F4+-+3%2Ad%2F4%29+%2B+1%5Cd+=+56\"   DISABLED_style= \"max-width:90%; height:auto;\" > and simplify: So, we know that d=20. Since <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=c+=+108%2F4+-+3%2Ad%2F4 ALIGN=MIDDLE  ALT=\"c+=+108%2F4+-+3%2Ad%2F4\"   DISABLED_style= \"max-width:90%; height:auto;\" >, c=12.<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  Answer: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+c=12%2C+d=20+%29 ALIGN=MIDDLE  ALT=\"system%28+c=12%2C+d=20+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "  </TD></TR>\n" );
document.write( "</TABLE><BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );