document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=5887>Question 5887</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Suppose you have a lemonade stand, and when you charge $1 per cup of lemonade you sell 60 cups.  But when you raise your price to $2 you only sell 30 cups.  Write an equation for the number of cups you sell  as a function of the price you charge.  Denote \"C\" for number of cups, and \"P\" for the price you charge.  Assume the function is linear.\r<BR>\n" );
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document.write( "I know this may seem really easy, but I have been looking at it forever and I can't figure it out. I want to help my cousin with his homework but it's above my head. Thanks for all your help.<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #3098 by </B><A HREF=/tutors/aboutme.mpl?userid=longjonsilver><B>longjonsilver(2297)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=longjonsilver><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=longjonsilver><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=3098\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> when P=1 --> C=60<BR>\n" );
document.write( "when P=2 --> C=30\r<BR>\n" );
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document.write( "imagine a grpah of C against P...just like y-against-x.\r<BR>\n" );
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document.write( "We have 2 coordinates (1, 60) and (2, 30). Now, assuming it is linear, we can find the gradient, m from:\r<BR>\n" );
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document.write( "m = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28y%5B2%5D+-+y%5B1%5D%29%2F%28x%5B2%5D+-+x%5B1%5D%29 ALIGN=MIDDLE  ALT=\"%28y%5B2%5D+-+y%5B1%5D%29%2F%28x%5B2%5D+-+x%5B1%5D%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "m = (60-30)/(1-2)<BR>\n" );
document.write( "m = 30/-1<BR>\n" );
document.write( "m = -30\r<BR>\n" );
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document.write( "so, from the general equation of a straight line, y=mx+c, we now know that y=-30x+c. Now for c. To find this, we need to know both \"x\" and \"y\"...which we do: we have 2 sets of points. So pick one of them..i chose (1,60):\r<BR>\n" );
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document.write( "60 = -30(1) + c<BR>\n" );
document.write( "60 = -30 + c<BR>\n" );
document.write( "c = 90\r<BR>\n" );
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document.write( "so, equation is now C = -30P + 90\r<BR>\n" );
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document.write( "jon.<BR>\n" );
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