document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1200265>Question 1200265</A>: <I><SPAN STYLE=\"word-break: break-all;\"> It took a crew 9 h 36 min to row 9 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 #834342 by </B><A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><B>math_tutor2020(3817)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=834342\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=black size=3><BR>\n" );
document.write( "9 hrs 36 min = 9.6 hrs<BR>\n" );
document.write( "since 36 min = 36/60 = 0.6 hrs\r<BR>\n" );
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document.write( "x = speed of the boat in still water<BR>\n" );
document.write( "where x > 7\r<BR>\n" );
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document.write( "When going upstream, the boat is slowed down to a speed of x-7 km/hr.<BR>\n" );
document.write( "When going downstream, the boat is sped up to a speed of x+7 km/hr.\r<BR>\n" );
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document.write( "Upstream:<BR>\n" );
document.write( "distance = rate*time<BR>\n" );
document.write( "9 = (x-7)*t1<BR>\n" );
document.write( "t1 = 9/(x-7)<BR>\n" );
document.write( "It takes 9/(x-7) hours to row upstream.\r<BR>\n" );
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document.write( "Downstream:<BR>\n" );
document.write( "distance = rate*time<BR>\n" );
document.write( "9 = (x+7)*t2<BR>\n" );
document.write( "t2 = 9/(x+7)<BR>\n" );
document.write( "It takes 9/(x+7) hours to row downstream.\r<BR>\n" );
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document.write( "The two time values (t1 and t2) must add to the total 9.6 hours mentioned earlier.<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=t%5B1%5D%2Bt%5B2%5D+=+9.6 ALIGN=MIDDLE  ALT=\"t%5B1%5D%2Bt%5B2%5D+=+9.6\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=9%2F%28x-7%29%2B9%2F%28x%2B7%29+=+9.6 ALIGN=MIDDLE  ALT=\"9%2F%28x-7%29%2B9%2F%28x%2B7%29+=+9.6\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=9%28x%2B7%29%2B9%28x-7%29+=+9.6%28x-7%29%28x%2B7%29 ALIGN=MIDDLE  ALT=\"9%28x%2B7%29%2B9%28x-7%29+=+9.6%28x-7%29%28x%2B7%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > Multiply both sides by the LCD (x-7)(x+7) to clear out the fractions.\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=9x%2B63%2B9x-63+=+9.6x%5E2-470.4 ALIGN=MIDDLE  ALT=\"9x%2B63%2B9x-63+=+9.6x%5E2-470.4\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=12%288x%5E2-15x-392%29+=+0 ALIGN=MIDDLE  ALT=\"12%288x%5E2-15x-392%29+=+0\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=8x%5E2-15x-392+=+0 ALIGN=MIDDLE  ALT=\"8x%5E2-15x-392+=+0\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "We have an equation in the form ax^2+bx+c = 0<BR>\n" );
document.write( "a = 8<BR>\n" );
document.write( "b = -15<BR>\n" );
document.write( "c = -392<BR>\n" );
document.write( "Plug those into the quadratic formula.<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%2815%2B113%29%2F%2816%29 ALIGN=MIDDLE  ALT=\"x+=+%2815%2B113%29%2F%2816%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%2815-113%29%2F%2816%29 ALIGN=MIDDLE  ALT=\"x+=+%2815-113%29%2F%2816%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28128%29%2F%2816%29 ALIGN=MIDDLE  ALT=\"x+=+%28128%29%2F%2816%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > or  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-98%29%2F%2816%29 ALIGN=MIDDLE  ALT=\"x+=+%28-98%29%2F%2816%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+8 ALIGN=MIDDLE  ALT=\"x+=+8\"   DISABLED_style= \"max-width:90%; height:auto;\" > or  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+-6.125 ALIGN=MIDDLE  ALT=\"x+=+-6.125\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "A negative speed value doesn't make sense, so we ignore <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+-6.125 ALIGN=MIDDLE  ALT=\"x+=+-6.125\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "The only practical answer is <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+8 ALIGN=MIDDLE  ALT=\"x+=+8\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "Answer: The speed of the boat in still water is 8 km/hr.<BR>\n" );
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