document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=76869>Question 76869</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I am very stuck can someone pleas help me?<BR>\n" );
document.write( "Science and medicine. A plane flies 720 mi against a steady 30-mi/h headwind<BR>\n" );
document.write( "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 #55272 by </B><A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><B>ankor@dixie-net.com(22740)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><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=ankor@dixie-net.com><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=55272\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the<BR>\n" );
document.write( " same point with the wind. If the entire trip takes 10 h, what is the plane’s speed in still air?<BR>\n" );
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document.write( "Not hard if you follow a logical procedure:<BR>\n" );
document.write( "Let s = planes speed in still air:<BR>\n" );
document.write( "Then:<BR>\n" );
document.write( "(s-30) = speed against the wind<BR>\n" );
document.write( "(s+30 = speed with the wind<BR>\n" );
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document.write( "Write a time equation: Time = dist/speed<BR>\n" );
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document.write( "Time out + time back = 10 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=720%2F%28%28s-30%29%29 ALIGN=MIDDLE  ALT=\"720%2F%28%28s-30%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=720%2F%28%28s%2B30%29%29 ALIGN=MIDDLE  ALT=\"720%2F%28%28s%2B30%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 10<BR>\n" );
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document.write( "Mult equation by (s-3)(s+30) to get rid of the denominators:<BR>\n" );
document.write( "720(s+30) + 720(s-30) = 10(s-30)(s+30)<BR>\n" );
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document.write( "720s + 21600 + 720s - 21600 = 10(s^2 - 900)<BR>\n" );
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document.write( "1440s = 10s^2 - 9000<BR>\n" );
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document.write( "0 = 10s^2 - 1440s - 9000<BR>\n" );
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document.write( "Simplify, divide equation by 10; a simple quadratic equation:<BR>\n" );
document.write( "s^2 - 144s - 900 = 0<BR>\n" );
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document.write( "This will factor to:<BR>\n" );
document.write( "(s - 150)(s + 6) = 0<BR>\n" );
document.write( "s = +150, this is the solution we want<BR>\n" );
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document.write( "Plane speed in still air is 150 mph><BR>\n" );
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document.write( "Check:<BR>\n" );
document.write( "against the wind: 720/120 = 6 hrs<BR>\n" );
document.write( "With the wind is: 720/180 = 4 hrs<BR>\n" );
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document.write( "Total round trip time is = 10 hrs<BR>\n" );
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document.write( "How about it, did this make sense to you? </SPAN>\n" );
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