document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1034987>Question 1034987</A>: <I><SPAN STYLE=\"word-break: break-all;\"> It took a crew 8 h 32 min to row 8 km upstream and back again. If the rate of flow of the stream was 7 km/h, what was 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 #649673 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=649673\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> It took a crew 8 h 32 min to row 8 km upstream and back again.<BR>\n" );
document.write( " If the rate of flow of the stream was 7 km/h, what was the rowing speed of the crew in still water?<BR>\n" );
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document.write( "Let s = rowing speed in still water.<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s-7) = effective speed upstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s+7) = effective speed downstream <BR>\n" );
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document.write( "Change 8 hrs 32 min to hrs: 8 + 32/60 = 8 + 8/15 hrs = 128/15<BR>\n" );
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document.write( " write a time equation, time = dist/speed<BR>\n" );
document.write( "Time up + time down = 8hr 32 min<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=8%2F%28%28s-7%29%29 ALIGN=MIDDLE  ALT=\"8%2F%28%28s-7%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=8%2F%28%28s%2B7%29%29 ALIGN=MIDDLE  ALT=\"8%2F%28%28s%2B7%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=128%2F15 ALIGN=MIDDLE  ALT=\"128%2F15\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "simplify, divide by 8<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1%2F%28%28s-7%29%29 ALIGN=MIDDLE  ALT=\"1%2F%28%28s-7%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1%2F%28%28s%2B7%29%29 ALIGN=MIDDLE  ALT=\"1%2F%28%28s%2B7%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=16%2F15 ALIGN=MIDDLE  ALT=\"16%2F15\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "multiply by 15(s-7)(s+7), cancel the denominators<BR>\n" );
document.write( " 15(s+7) + 15(s-7) = (s-7)(s+7)*16<BR>\n" );
document.write( " 15s + 105 + 15s - 105 = 16(s^2 - 49)<BR>\n" );
document.write( " 30s = 16s^2 - 784<BR>\n" );
document.write( "0 = 16s^2 - 30s - 784<BR>\n" );
document.write( "simplify, divide by 2<BR>\n" );
document.write( "8s^2 - 15s - 392 = 0<BR>\n" );
document.write( "you can use the quadratic formula, but this will factor to<BR>\n" );
document.write( "(8s+49)(s-8) = 0<BR>\n" );
document.write( "the positive solution is all we want here<BR>\n" );
document.write( "s = 8 km/hr in still water<BR>\n" );
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document.write( "See if that checks out. Find the actual time each way<BR>\n" );
document.write( "8/(8-7) = 8 hrs upstream<BR>\n" );
document.write( "8/(8+7) = .533 hrs which is 32 min down stream </SPAN>\n" );
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