document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1151880>Question 1151880</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Build the equation for the number of DVDs, n, In terms of their Price, P.<BR>\n" );
document.write( "One month a store sells dvds for $5 Each and sells 1200 DVDs. The next month they charge $7.50 and sell 800 dvds </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #773738 by </B><A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><B>jim_thompson5910(35256)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=773738\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=black size=3><BR>\n" );
document.write( "Temporarily, I'm going to use x instead of P. <BR>\n" );
document.write( "Also, I'll use y in place of n. <BR>\n" );
document.write( "At the end I'll do replacements.\r<BR>\n" );
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document.write( "x = price<BR>\n" );
document.write( "y = number of DVDs\r<BR>\n" );
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document.write( "\"One month a store sells dvds for $5 Each and sells 1200 DVDs.\" means we have the point (x1,y1) = (5, 1200)\r<BR>\n" );
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document.write( "\"The next month they charge $7.50 and sell 800 dvds\" means we have the point (x2,y2) = (7.5, 800)\r<BR>\n" );
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document.write( "Calculate the slope<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=m+=+%28y%5B2%5D+-+y%5B1%5D%29%2F%28x%5B2%5D+-+x%5B1%5D%29 ALIGN=MIDDLE  ALT=\"m+=+%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( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=m+=+%28800+-+1200%29%2F%287.5+-+5%29 ALIGN=MIDDLE  ALT=\"m+=+%28800+-+1200%29%2F%287.5+-+5%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=m+=+%28-400%29%2F%282.5%29 ALIGN=MIDDLE  ALT=\"m+=+%28-400%29%2F%282.5%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=m+=+-160 ALIGN=MIDDLE  ALT=\"m+=+-160\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "The slope tells us that for each price increase of $1, the number of DVDs sold goes down by 160.\r<BR>\n" );
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document.write( "Now turn to the point-slope formula. Plug in the given info. Solve for y.<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y-y%5B1%5D+=+m%28x+-+x%5B1%5D%29 ALIGN=MIDDLE  ALT=\"y-y%5B1%5D+=+m%28x+-+x%5B1%5D%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y-1200+=+-160%28x+-+5%29 ALIGN=MIDDLE  ALT=\"y-1200+=+-160%28x+-+5%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y-1200+=+-160%28x%29+-+160%28-5%29 ALIGN=MIDDLE  ALT=\"y-1200+=+-160%28x%29+-+160%28-5%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y-1200+=+-160x+%2B+800 ALIGN=MIDDLE  ALT=\"y-1200+=+-160x+%2B+800\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y+=+-160x+%2B+800%2B1200 ALIGN=MIDDLE  ALT=\"y+=+-160x+%2B+800%2B1200\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y+=+-160x%2B2000 ALIGN=MIDDLE  ALT=\"y+=+-160x%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2AP%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2AP%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" > Replace x with P, replace y with n.\r<BR>\n" );
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document.write( "Check: \r<BR>\n" );
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document.write( "We should plug in a price of P = 5 and get n = 1200<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2AP%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2AP%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2A5%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2A5%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-800%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-800%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+1200 ALIGN=MIDDLE  ALT=\"n+=+1200\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "so that works out. Also, plugging in P = 7.5 should lead to n = 800<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2AP%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2AP%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2A7.5%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2A7.5%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-1200%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-1200%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+800 ALIGN=MIDDLE  ALT=\"n+=+800\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "that works as well. We have the proper equation.\r<BR>\n" );
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document.write( "Answer: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=n+=+-160%2AP%2B2000 ALIGN=MIDDLE  ALT=\"n+=+-160%2AP%2B2000\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "</font> </SPAN>\n" );
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