document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=941339>Question 941339</A>: <I><SPAN STYLE=\"word-break: break-all;\"> It took a crew 2.75 hours to row 6 km upstream and back again (6 km one way ). If the rate of flow of the stream was 3 km/hr, what would be the rowing speed of the crew 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 #573822 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=573822\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> It took a crew 2.75 hours to row 6 km upstream and back again (6 km one way <BR>\n" );
document.write( "If the rate of flow of the stream was 3 km/hr, what would be the rowing speed of the crew in still water?<BR>\n" );
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document.write( "Let s = their speed in still water<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s+3) = effective speed downstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s-3) = effective speed upstream<BR>\n" );
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document.write( "Write time equation; time = dist/speed<BR>\n" );
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document.write( "time upstr + time downstr = 2.75 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=6%2F%28s%2B3%29 ALIGN=MIDDLE  ALT=\"6%2F%28s%2B3%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=6%2F%28s-3%29 ALIGN=MIDDLE  ALT=\"6%2F%28s-3%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 2.75<BR>\n" );
document.write( ":<BR>\n" );
document.write( "multiply equation by (s-3)(s+3)<BR>\n" );
document.write( "(s+3)(s-3)*<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=6%2F%28s%2B3%29 ALIGN=MIDDLE  ALT=\"6%2F%28s%2B3%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + (s+3)(s-3)*<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=6%2F%28s-3%29 ALIGN=MIDDLE  ALT=\"6%2F%28s-3%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 2.75(s+3)(s-3)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Cancel the denominator, FOIL the right side<BR>\n" );
document.write( "6(s-3) + 6(s+3) = 2.75(s^2-3s+3s-9)<BR>\n" );
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document.write( "distribute. combine like terms<BR>\n" );
document.write( "6s - 18 + 6s + 18 = 2.75(s^2-9)<BR>\n" );
document.write( "12s = 2.75s^2 - 24.75<BR>\n" );
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document.write( "A Quadratic equation<BR>\n" );
document.write( "0 = 2.75s^2 - 12s - 24.75<BR>\n" );
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document.write( "Use the quadratic formula, a=2.75; b=-12; c=-24.75<BR>\n" );
document.write( "I got a positive solution of:<BR>\n" );
document.write( "s = 5.89 km in still water<BR>\n" );
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document.write( ";<BR>\n" );
document.write( "Confirm this; find the actual time each way<BR>\n" );
document.write( "6/2.89 = 2.08 hrs upstream (3 km/hr slower)<BR>\n" );
document.write( "6/8.89 = 0.67 hrs downstream (3 km/hr faster)<BR>\n" );
document.write( "---------------------------<BR>\n" );
document.write( "total: 2.75 hrs<BR>\n" );
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document.write( "Did this make sense to you?<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );