document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=48366>Question 48366</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A plane flies 720 miles against a steady 30 mile per hour headwind and then returns to the same point with the wind. If the entire trip takes 10 hours, what is the plane's speed in still air? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #32009 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=32009\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A plane flies 720 miles against a steady 30 mile per hour headwind and then returns to the same point with the wind. If the entire trip takes 10 hours, what is the plane's speed in still air?<BR>\n" );
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document.write( "Let \"p\" be plane speed without wind.<BR>\n" );
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document.write( "With the wind DATA:<BR>\n" );
document.write( "distance=720 mi ; rate= p+30 mph ; time = d/r = 720/(p+30) hr.<BR>\n" );
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document.write( "Against the wind DATA:<BR>\n" );
document.write( "distance=720 mi ; rate = p-30 mph ; time =d/r = 720(p-30) hr.<BR>\n" );
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document.write( "EQUATION:<BR>\n" );
document.write( "time + time = 10 hrs<BR>\n" );
document.write( "720/(p+30) + 720/(p-30) = 10<BR>\n" );
document.write( "72/(p+30) + 72/(p-30) = 1<BR>\n" );
document.write( "72p + 72p = p^2-900<BR>\n" );
document.write( "p^2-144p-900=0<BR>\n" );
document.write( "(p-150)(p+6)=0<BR>\n" );
document.write( "p=150 mph (The plane's speed in still air is 150 mph)\r<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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