document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=818371>Question 818371</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Devante flies a plane against a headwind for 3168 miles. The return trip with the wind took 18 hours less time. If the wind speed is 9 mph, how fast does Devante fly the plane when there is no wind? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #492495 by </B><A HREF=/tutors/aboutme.mpl?userid=TimothyLamb><B>TimothyLamb(4379)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=TimothyLamb><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=TimothyLamb><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=492495\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> s = d / t<BR>\n" );
document.write( "d = s * t<BR>\n" );
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document.write( "outbound:<BR>\n" );
document.write( "3168 = (s - w)T<BR>\n" );
document.write( "---<BR>\n" );
document.write( "return:<BR>\n" );
document.write( "3168 = (s + w)(T - 18)<BR>\n" );
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document.write( "(s - w)T = (s + w)(T - 18)<BR>\n" );
document.write( "(s - 9)T = (s + 9)(T - 18)<BR>\n" );
document.write( "sT - 9T = sT - 18s + 9T - 162<BR>\n" );
document.write( "0 = -18s + 18T - 162<BR>\n" );
document.write( "18T - 18s = 162<BR>\n" );
document.write( "18(T - s) = 162<BR>\n" );
document.write( "T - s = 9<BR>\n" );
document.write( "s = T - 9<BR>\n" );
document.write( "---<BR>\n" );
document.write( "3168 = (s - w)T<BR>\n" );
document.write( "3168 = (s - 9)T<BR>\n" );
document.write( "3168 = (T - 9 - 9)T<BR>\n" );
document.write( "3168 = (T - 18)T<BR>\n" );
document.write( "TT - 18T - 3168 = 0<BR>\n" );
document.write( "T^2 - 18T - 3168 = 0<BR>\n" );
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document.write( "the above quadratic equation is in standard form, with a=1, b=-18, and c=-3168<BR>\n" );
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document.write( "to solve the quadratic equation, by using the quadratic formula, plug this:<BR>\n" );
document.write( "1 -18 -3168<BR>\n" );
document.write( "into this: https://sooeet.com/math/quadratic-equation-solver.php<BR>\n" );
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document.write( "the two real roots (i.e. the two x-intercepts), of the quadratic are:<BR>\n" );
document.write( "T = 66<BR>\n" );
document.write( "T = -48<BR>\n" );
document.write( "---<BR>\n" );
document.write( "the negative root doesn't make sense for time, so use the positive root:<BR>\n" );
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document.write( "T = 66 hours<BR>\n" );
document.write( "s = T - 9<BR>\n" );
document.write( "s = 66 - 9<BR>\n" );
document.write( "---<BR>\n" );
document.write( "answer:<BR>\n" );
document.write( "airplane speed in calm air: s = 57 mph<BR>\n" );
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document.write( "Solve and graph linear equations:<BR>\n" );
document.write( "https://sooeet.com/math/linear-equation-solver.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Solve quadratic equations, quadratic formula:<BR>\n" );
document.write( "https://sooeet.com/math/quadratic-formula-solver.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Convert fractions, decimals, and percents:<BR>\n" );
document.write( "https://sooeet.com/math/fraction-decimal-percent.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Calculate and graph the linear regression of any data set:<BR>\n" );
document.write( "https://sooeet.com/math/linear-regression.php </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );