document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=90884>Question 90884</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, 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 #65968 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=65968\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane’s speed in still air?<BR>\n" );
document.write( "--------------<BR>\n" );
document.write( "Let the speed of the plane in calm air be \"p\".<BR>\n" );
document.write( "---------------------<BR>\n" );
document.write( "Against the wind DATA:<BR>\n" );
document.write( "distance = 720 mi ; rate = p-30 ; time = d/r = 720/(p-30)<BR>\n" );
document.write( "---------------<BR>\n" );
document.write( "With the wind DATA;<BR>\n" );
document.write( "distance = 720 mi ; rate = p+30 ; time = d/r = 720/(p+30)<BR>\n" );
document.write( "------------------<BR>\n" );
document.write( "EQUATION:<BR>\n" );
document.write( "time + 1ime = 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( "Multiply thru by P^2-900 to get:<BR>\n" );
document.write( "72(p+30) + 72(p-30) = p^2-900<BR>\n" );
document.write( "144p= p^2-900<BR>\n" );
document.write( "p^2-144p-900 = 0<BR>\n" );
document.write( "(p+6)(p-150)=0<BR>\n" );
document.write( "p = 150 mph (speed of the plane in still air)<BR>\n" );
document.write( "===============<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );