document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=372437>Question 372437</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The Stemsell River flows at a rate of 4Km/h. In order for a boat to travel 33.6 km upriver and then return in a total of 8 hr, how fast must the boat travel in still water? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #265320 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=265320\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The Stemsell River flows at a rate of 4Km/h.<BR>\n" );
document.write( " In order for a boat to travel 33.6 km upriver and then return in a total of 8 hr, <BR>\n" );
document.write( "how fast must the boat travel in still water?<BR>\n" );
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document.write( "Let s = boat speed in still water<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s-4) = effective speed upstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s+4) = effective speed downstream<BR>\n" );
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document.write( "Write a time equation: time = dist/speed<BR>\n" );
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document.write( "time upstream + time downstream = 8 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=33.6%2F%28%28s-4%29%29 ALIGN=MIDDLE  ALT=\"33.6%2F%28%28s-4%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=33.6%2F%28%28s%2B4%29%29 ALIGN=MIDDLE  ALT=\"33.6%2F%28%28s%2B4%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 8<BR>\n" );
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document.write( "multiply by (s-4)(s+4), to clear the denominator, results<BR>\n" );
document.write( "33.6(s+4) + 33.6(s-4) = 8(s+4)(s-4)<BR>\n" );
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document.write( "33.6s + 134.4 + 33.6s - 134.4 = 8(s^2 - 16)<BR>\n" );
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document.write( "67.2s = 8s^2 - 128<BR>\n" );
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document.write( "A quadratic equation<BR>\n" );
document.write( "8s^2 - 67.2s - 128 = 0<BR>\n" );
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document.write( "simplify, divide by 8<BR>\n" );
document.write( "s^2 - 8.4s - 16<BR>\n" );
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document.write( "This will factor to:<BR>\n" );
document.write( "(x+1.6)(x-10) = 0<BR>\n" );
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document.write( "positive solution is what we want here:<BR>\n" );
document.write( "s = 10 km/hr in still water<BR>\n" );
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document.write( "Check this, find the time of each trip<BR>\n" );
document.write( "33.6/6 = 5.6 hrs<BR>\n" );
document.write( "33.6/14= 2.4 hrs<BR>\n" );
document.write( "----------------<BR>\n" );
document.write( "total time 8 hrs </SPAN>\n" );
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