document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1165967>Question 1165967</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The phone company Ringular has a monthly plan where a customer pays a flat monthly fee, and then a set rate per minute. If a customer uses 110 minutes, the monthly cost will be $84. If the customer uses 960 minutes, the monthly cost will be $424.<BR>\n" );
document.write( "Find the equation of the plan in the form y=mx+b<BR>\n" );
document.write( "xis the number of monthly minutes used and  <BR>\n" );
document.write( "yis the total monthly cost of the Ringular plan. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #790428 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=790428\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> at 110 minutes, the monthly cost is 84 dollars.<BR>\n" );
document.write( "at 960 minutes the monthly cost is 424 dollars.\r<BR>\n" );
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document.write( "straight line equation is y = mx + b.<BR>\n" );
document.write( "m is the slope.<BR>\n" );
document.write( "b is the y-intercept which is the value of y when x = 0.\r<BR>\n" );
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document.write( "you have two points to work with.<BR>\n" );
document.write( "in (x,y) format, they are (110,84) and (960,424).<BR>\n" );
document.write( "x represents the number of minutes.<BR>\n" );
document.write( "y represents the total cost for that number of minutes.\r<BR>\n" );
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document.write( "m is the slope which is equal to (y1-y1)/(x2-x1).<BR>\n" );
document.write( "let (110,84) = (x1,y1) and let (960,424) = (x2,y2).<BR>\n" );
document.write( "m = (424-84)/(960-110) = 340/850.<BR>\n" );
document.write( "simplify to get 2/5.\r<BR>\n" );
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document.write( "y = mx + b becomes y = 2/5 * x + b<BR>\n" );
document.write( "to find b, replace x and y with the values from one of the points.<BR>\n" );
document.write( "any one of the points will work.<BR>\n" );
document.write( "i chose (x2,y2) = (960,424)<BR>\n" );
document.write( "y = 2/5 * x + b becomes 424 = 2/5 * 960 + b<BR>\n" );
document.write( "solve for b to get:<BR>\n" );
document.write( "b = 40\r<BR>\n" );
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document.write( "y = mx + b becomes y = 2/5 * x + 40\r<BR>\n" );
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document.write( "test with the 2 known points.<BR>\n" );
document.write( "with x = 110, the equation becomes y = 2/5 * 110 + 40 = 84<BR>\n" );
document.write( "with x = 960, the equation becomes y = 2/5 * 960 + 40 = 424\r<BR>\n" );
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document.write( "the equation you are looking for is confirmed to be y = 2/5 * x + 40<BR>\n" );
document.write( "x is the number of minutes consumed per month.<BR>\n" );
document.write( "y is the total cost per month.<BR>\n" );
document.write( "there is a flat monthly fee of 40 dollars.<BR>\n" );
document.write( "the cost per minute is 2/5 = .40 dollars = 40 cents. </SPAN>\n" );
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