document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=37555>Question 37555</A>: <I><SPAN STYLE=\"word-break: break-all;\"> If it costs $65 to travel 200km on a train and $80 to travel 350km, then;<BR>\n" );
document.write( "a) express the cost, y, as a linear equation of distance traveled, x.<BR>\n" );
document.write( "b) accordingly, how much would it cost to travel 500 km?\r<BR>\n" );
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document.write( "I have the answer which should be a) y= 0.010x + 45<BR>\n" );
document.write( "                                  b) $95\r<BR>\n" );
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document.write( "But have no idea how they got the answer.  Should I be assigning two variables x and y to represent the unknow values.  Write two equations using both variables and then solve the system of the given equations?<BR>\n" );
document.write( "Not quite sure where to begin?<BR>\n" );
document.write( "thank you<BR>\n" );
document.write( "claudia  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #23179 by </B><A HREF=/tutors/aboutme.mpl?userid=fractalier><B>fractalier(6550)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=fractalier><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=fractalier><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=23179\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> If we let x be km traveled and y be the cost (in $), we have been given two points, (x, y).  These points are (200, 65) and (350, 80).  We treat these as any two (x, y) points.  Let us first find the slope:<BR>\n" );
document.write( "m = (y2 - y1) / (x2 - x1)<BR>\n" );
document.write( "m = (80 - 65) / (350 - 200)<BR>\n" );
document.write( "m = 15 / 150<BR>\n" );
document.write( "m = 0.10<BR>\n" );
document.write( "Now we use the point slope form to get the equation of the line:<BR>\n" );
document.write( "y - y1 = m(x - x1)  now plug in<BR>\n" );
document.write( "y - 65 = .1(x - 200)<BR>\n" );
document.write( "y - 65 = .1x - 20<BR>\n" );
document.write( "y = .1x + 45<BR>\n" );
document.write( "This IS the correct answer, not what you have.  Notice the difference between .1 and .01<BR>\n" );
document.write( "b) Now plug in x = 500<BR>\n" );
document.write( "y = .1x + 45<BR>\n" );
document.write( "y = .1(500) + 45<BR>\n" );
document.write( "y = 50 + 45<BR>\n" );
document.write( "y = 95<BR>\n" );
document.write( "There you go... </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );