document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=15821>Question 15821</A>: <I><SPAN STYLE=\"word-break: break-all;\"> a boat travels 80km upstream and then returns to its starting point. The entire trip takes 3.6h. if the speed of the current is 10km/h, determine the speed of the boat 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 #7800 by </B><A HREF=/tutors/aboutme.mpl?userid=rapaljer><B>rapaljer(4671)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rapaljer><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=rapaljer><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=7800\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let x = speet of the boat in still water.<BR>\n" );
document.write( "x+10 = speed of the boat going downstream.<BR>\n" );
document.write( "x-10 = speed of the boat going upstream.\r<BR>\n" );
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document.write( "The equation is based upon the time of the boat to go upstream and then downstream.  \r<BR>\n" );
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document.write( "Time upstream = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=D%2Fr ALIGN=MIDDLE  ALT=\"D%2Fr\"   DISABLED_style= \"max-width:90%; height:auto;\" >    Time downstream = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=D%2Fr ALIGN=MIDDLE  ALT=\"D%2Fr\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "Total time = Time up + Time down = 3.6 hours<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=80%2F%28x-10%29+%2B+80%2F%28x%2B10%29+=+3.6+ ALIGN=MIDDLE  ALT=\"80%2F%28x-10%29+%2B+80%2F%28x%2B10%29+=+3.6+\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "Multiply both sides of the equation by the LCD = (x-10)(x+10), and the result is:\r<BR>\n" );
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document.write( "80(x+10) + 80(x-10) = 3.6(x-10)(x+10)\r<BR>\n" );
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document.write( "80x +800 + 80x - 800 = 3.6(x^2 - 100)<BR>\n" );
document.write( "160x = 3.6x^2 - 360\r<BR>\n" );
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document.write( "Set equal to zero, since it is a quadratic equation:<BR>\n" );
document.write( "0 = 3.6x^2 - 160x - 360\r<BR>\n" );
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document.write( "Use quadratic equation solver or calculator:\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28160+%2B-+sqrt%28+160%5E2%2B4%2A3.6%2A360+%29%29%2F%282%2A3.6%29+ ALIGN=MIDDLE  ALT=\"x+=+%28160+%2B-+sqrt%28+160%5E2%2B4%2A3.6%2A360+%29%29%2F%282%2A3.6%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" > <BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28160+%2B-+sqrt%2830784%29%29%2F+7.2+ ALIGN=MIDDLE  ALT=\"x+=+%28160+%2B-+sqrt%2830784%29%29%2F+7.2+\"   DISABLED_style= \"max-width:90%; height:auto;\" > <BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28160+%2B-+175.4537%29%2F7.2+ ALIGN=MIDDLE  ALT=\"x+=+%28160+%2B-+175.4537%29%2F7.2+\"   DISABLED_style= \"max-width:90%; height:auto;\" > (approximately!)\r<BR>\n" );
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document.write( "x must be a postive number, so forget the negative value,<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x=+%28160+%2B+175.4537%29%2F7.2 ALIGN=MIDDLE  ALT=\"x=+%28160+%2B+175.4537%29%2F7.2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+46.49+ ALIGN=MIDDLE  ALT=\"x+=+46.49+\"   DISABLED_style= \"max-width:90%; height:auto;\" >mph in still water.<BR>\n" );
document.write( "x+10 = 56.49 mph downstream<BR>\n" );
document.write( "x-10 = 36.49 mph upstream\r<BR>\n" );
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document.write( "As a check, calculate the equation for time upstream and downstream:<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=80%2F36.49+%2B+80%2F56.49 ALIGN=MIDDLE  ALT=\"80%2F36.49+%2B+80%2F56.49\"   DISABLED_style= \"max-width:90%; height:auto;\" >.  The answer comes out to about 3.6 hours.\r<BR>\n" );
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document.write( "R^2 at SCC\r<BR>\n" );
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document.write( " </SPAN>\n" );
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