document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1128013>Question 1128013</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The rate at which water evaporates from a certain reservoir depends on the air temperature. The table below shows the number of acre-feet (af) of water per day that evaporates from the reservoir for various temperatures in degrees Fahrenheit. <BR>\n" );
document.write( "Temperature (°F)     (af) <BR>\n" );
document.write( "40                    960 <BR>\n" );
document.write( "60                    1800 <BR>\n" );
document.write( "70                    2220 <BR>\n" );
document.write( "85                    2850 <BR>\n" );
document.write( "(a) Find a linear model for the number of acre-feet of water that evaporates as a function of temperature. <BR>\n" );
document.write( "E(T) =<BR>\n" );
document.write( "(b) Explain the meaning of the slope of this line in the context of this problem. <BR>\n" );
document.write( "The value of the slope means that an additional  af evaporates for a 1°F  in temperature. <BR>\n" );
document.write( "(c) Assuming that water continues to evaporate at the same rate, how many acre-feet of water will evaporate per day when the temperature is 75°F? <BR>\n" );
document.write( " af  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #744650 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=744650\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> slope is change in y/change in x<BR>\n" );
document.write( "840/20=42, and that is the slope between any two adjacent points.<BR>\n" );
document.write( "use point slope formula for the model y-y1=m(x-x1) m slope and (x1, y1) point<BR>\n" );
document.write( "y-960=42(x-40)<BR>\n" );
document.write( "y=42x-720<BR>\n" );
document.write( "E(T)=42 F - 720<BR>\n" );
document.write( "every degree change F increases acre-feet evaporation by 42 af a day.<BR>\n" );
document.write( "at 75 degrees it will be 42*75-720 or 2430 af  a day.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=graph%28300%2C300%2C-10%2C80%2C-500%2C3000%2C42x-720%29 ALIGN=MIDDLE  ALT=\"graph%28300%2C300%2C-10%2C80%2C-500%2C3000%2C42x-720%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );