document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=291768>Question 291768</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The variable of z varies jointly with x and y. Also, z=120 when x=-5 and y=-2. Write an equation that relates x, y and z. Then find z when x=-5 and y = -4. Equation of z = value of z =  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #210912 by </B><A HREF=/tutors/aboutme.mpl?userid=richwmiller><B>richwmiller(17219)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=richwmiller><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=richwmiller><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=210912\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Your problem didn't say whether it varies directly or inversely.<BR>\n" );
document.write( "I will assume directly<BR>\n" );
document.write( "z=kxy<BR>\n" );
document.write( "120=k*(-5)*(-2)<BR>\n" );
document.write( "120=10k<BR>\n" );
document.write( "k=12<BR>\n" );
document.write( "z=12xy<BR>\n" );
document.write( "z=12*(-5)*(-4)<BR>\n" );
document.write( "z=12*20<BR>\n" );
document.write( "z=240<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );