document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=320409>Question 320409</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Zelon Pharmaceuticals maintains a courier plane to transport company executives back and forth between the company headquarters and the main manufacturing plant 250 miles away. Today the pilot flew from headquarters to the plant, picked up the Chief of Operations, and returned to headquarters. On the first leg of the trip, the pilot flew against a headwind averaging 10 miles per hour. On the return leg, the average tailwind was 30 miles per hour. If the pilot spent a total of four hours in the air, what would the average speed of the courier plane be with no wind? Round your answer to the nearest mile per hour. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #229481 by </B><A HREF=/tutors/aboutme.mpl?userid=mananth><B>mananth(16946)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=mananth><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=mananth><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=229481\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let the speed in still air be x mph<BR>\n" );
document.write( "..<BR>\n" );
document.write( "250/x-10 +250/x+30 =4<BR>\n" );
document.write( "(x-10)(x+30) is the LCM<BR>\n" );
document.write( "250(x+30)+250(x-10)/ (x-10(x+30)=4<BR>\n" );
document.write( "250x+7500+250x-2500 = 4(x-10)(x+30)<BR>\n" );
document.write( "500x+5000=4(x^2+30x-10x-300)<BR>\n" );
document.write( "500x+5000=4x^2+120x-40x-1200<BR>\n" );
document.write( "4x^2-420x-6200=0<BR>\n" );
document.write( "x^2-105x-1550=0<BR>\n" );
document.write( "..<BR>\n" );
document.write( "Find the roots of the equation<BR>\n" );
document.write( "x1, x2<BR>\n" );
document.write( "..<BR>\n" );
document.write( "x1= +420 +sqrt((-420)^2-4*4(-6200)))/2*4<BR>\n" );
document.write( "=118.1 mph<BR>\n" );
document.write( "x2=+420 -sqrt((-420)^2-4*4(-6200)))/2*4<BR>\n" );
document.write( "x2=-13.1<BR>\n" );
document.write( "Ignore the negative value.<BR>\n" );
document.write( "so the speed in still air = 118.1 mph<BR>\n" );
document.write( "..<BR>\n" );
document.write( "CHECK<BR>\n" );
document.write( "(250/118.1-10)+(250/118.1+30)= 4.004 </SPAN>\n" );
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