document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=188935>Question 188935</A>: <I><SPAN STYLE=\"word-break: break-all;\"> An airplane took 2 hours to fly 600 km against a head wind.  The retrun trip with the wind took 1 and two thirds hours.  Find the speed of the plane in stll air. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #141769 by </B><A HREF=/tutors/aboutme.mpl?userid=jonvaliente><B>jonvaliente(64)</B></A><img src=\"/images/stars/stars-08.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jonvaliente><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=jonvaliente><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=141769\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let x=speed of the plane in still air<BR>\n" );
document.write( "    y=speed of the head wind<BR>\n" );
document.write( "    distance=speed * time\r<BR>\n" );
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document.write( "Against the head wind, the speed of the plane is x-y:\r<BR>\n" );
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document.write( "(x-y)*2=600          (1)\r<BR>\n" );
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document.write( "With the wind, the speed of the plane is x+y:\r<BR>\n" );
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document.write( "(x+y)*(5/3)=600      (2)\r<BR>\n" );
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document.write( "Simplifying (1) and (2) we get:\r<BR>\n" );
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document.write( "2x-2y=600            (1)<BR>\n" );
document.write( "(5/3)x+(5/3)y=600    (2)\r<BR>\n" );
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document.write( "Equating (1) and (2)\r<BR>\n" );
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document.write( "2x-2y=(5/3)x+(5/3)y\r<BR>\n" );
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document.write( "Multiply both sides by 3\r<BR>\n" );
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document.write( "(2x-2y)*3=((5/3)x+(5/3)y)*3\r<BR>\n" );
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document.write( "6x-6y=5x+5y\r<BR>\n" );
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document.write( "Solving for x we get:\r<BR>\n" );
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document.write( "x=11y         (3)\r<BR>\n" );
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document.write( "Substituting 11y for x in (1) we get:\r<BR>\n" );
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document.write( "((11y)-y)*2=600<BR>\n" );
document.write( "10y*2=600<BR>\n" );
document.write( "20y=600<BR>\n" );
document.write( "y=30\r<BR>\n" );
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document.write( "Solving for x using (3)\r<BR>\n" );
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document.write( "x=11(30)<BR>\n" );
document.write( "x=330\r<BR>\n" );
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document.write( "The speed of the plane in still air is 330kph<BR>\n" );
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