document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=126141>Question 126141</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I am completely lost on this problem can you please explain?\r<BR>\n" );
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document.write( "A sales person observes that if an item is priced at $6 per item then 4 items are sold. If it is priced at $8 per item, 2 items are sold. Find an equation to model the number y of items sold for x dollars per item. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #92443 by </B><A HREF=/tutors/aboutme.mpl?userid=marcsam823><B>marcsam823(57)</B></A><img src=\"/images/stars/stars-08.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=marcsam823><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=92443\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The primary goal of this problem is to find the equation of a line. This is expressed as y = mx + b, where m is the slope of the line and b is the y-intercept (where the line crosses the y axis).\r<BR>\n" );
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document.write( "If we remove the \"disguises\" of dollars and number of items we are simply left with two x-coordinates and two y-coordinates as shown in the chart below:\r<BR>\n" );
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document.write( "x | y<BR>\n" );
document.write( "_____<BR>\n" );
document.write( "6 | 4<BR>\n" );
document.write( "8 | 2\r<BR>\n" );
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document.write( "1. To find the slope of this line:<BR>\n" );
document.write( "m = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28y2+-+y1%29%2F%28x2+-+x1%29 ALIGN=MIDDLE  ALT=\"%28y2+-+y1%29%2F%28x2+-+x1%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%284+-+2%29%2F%286+-+8%29 ALIGN=MIDDLE  ALT=\"%284+-+2%29%2F%286+-+8%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=2%2F-2 ALIGN=MIDDLE  ALT=\"2%2F-2\"   DISABLED_style= \"max-width:90%; height:auto;\" > = -1 <BR>\n" );
document.write( "Using y = mx + b:<BR>\n" );
document.write( "      y = -1x + b\r<BR>\n" );
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document.write( "2. Substitute for x and y (plug in either of the two points - we'll use (6,4)):<BR>\n" );
document.write( "      y = mx + b<BR>\n" );
document.write( "      4 = -1(6) + b<BR>\n" );
document.write( "3. Find the y-intercept by solving for b:<BR>\n" );
document.write( "      4 = -6 + b<BR>\n" );
document.write( "      b = 10<BR>\n" );
document.write( "The equation is:<BR>\n" );
document.write( "      y = -x + 10\r<BR>\n" );
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document.write( "Check:<BR>\n" );
document.write( "Point (6,4)<BR>\n" );
document.write( "      4 = -(6) + 10 <BR>\n" );
document.write( "      4 = 4<BR>\n" );
document.write( "Point (8,2)<BR>\n" );
document.write( "      2 = -(8) + 10<BR>\n" );
document.write( "      2 = 2\r<BR>\n" );
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document.write( " </SPAN>\n" );
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