document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1114741>Question 1114741</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 20.\r<BR>\n" );
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document.write( "Suppose that income is a function of age. The following function represents the relation between average annual income l and age a.<BR>\n" );
document.write( " l(a)=-55a^2+5117a-54,421\r<BR>\n" );
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document.write( "(A) For what age does average income l equal $40,000?<BR>\n" );
document.write( "(B) For what age does average income l equal $60,000?\r<BR>\n" );
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document.write( "(a) Average income l is equal $40,000 for the age of?\r<BR>\n" );
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document.write( "(b) Average income l is equal $60,000 for the age of? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #729657 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13203)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><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=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=729657\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "The graph is a downward opening parabola, so it is likely that there will be two different ages for which the average income is $40,000 and two other different ages for which it is $60,000.<br><BR>\n" );
document.write( "With \"ugly\" coefficients like in this problem, you don't want to be solving the problem with pencil and paper.  Use a graphing calculator or some other mathematical tool to solve the problem.<br><BR>\n" );
document.write( "I use a TI83 graphing calculator; I can graph the given equation and the two constant functions 40000 and 60000 and find where the graphs intersect.<br><BR>\n" );
document.write( "Here is what the graph should look like....<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=graph%28400%2C400%2C0%2C80%2C-20000%2C100000%2C-55x%5E2%2B5117x-54421%2C40000%2C60000%29 ALIGN=MIDDLE  ALT=\"graph%28400%2C400%2C0%2C80%2C-20000%2C100000%2C-55x%5E2%2B5117x-54421%2C40000%2C60000%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "Apparently the average income is $40,000 at about ages 24 and 68; it is $60,000 at about ages 36 and 54. </SPAN>\n" );
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