document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=251327>Question 251327</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Sandy can swim 1 mile upstream in 20 minutes. She can swim the same distance downstream in 9 minutes. Find the speed of the current and of Sandy if both stay constant. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #182995 by </B><A HREF=/tutors/aboutme.mpl?userid=solver91311><B>solver91311(24713)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=solver91311><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=solver91311><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=182995\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font face=\"Garamond\" size=\"+2\">\r<BR>\n" );
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document.write( "Let <IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\Large r_S\"> represent her speed in still water and let <IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\Large r_c\"> represent the speed of the current.\r<BR>\n" );
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document.write( "Since we know that distance equals rate times time, 20 minutes is one-third of an hour, 9 minutes is 3/20ths of an hour, her speed relative to dry land upstream (against the current) must be <IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\Large r_S\ -\ r_c\">, and the speed downstream must be <IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\Large r_S\ +\ r_c\">, we can say the following things:\r<BR>\n" );
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document.write( "With respect to the upstream trip:\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\LARGE \ \ \ \ \ \ \ \ \ \  \left(r_S\ -\ r_c\right)\left(\frac{1}{3}\right)\ =\ 1\">\r<BR>\n" );
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document.write( "And with respect to the downstream trip:\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\LARGE \ \ \ \ \ \ \ \ \ \  \left(r_S\ +\ r_c\right)\left(\frac{3}{20}\right)\ =\ 1\">\r<BR>\n" );
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document.write( "A little arithmetic:\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\LARGE \ \ \ \ \ \ \ \ \ \  r_S\ -\ r_c\ =\ 3\">\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\LARGE \ \ \ \ \ \ \ \ \ \  r_S\ +\ r_c\ =\ \frac{20}{3}\">\r<BR>\n" );
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document.write( "Now all you need to do is solve the linear system.  The coordinates of the single ordered pair in the solution set are the answers you seek.\r<BR>\n" );
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document.write( "John<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=\"/cgi-bin/rendertex.cgi?\LARGE e^{i\pi} + 1 = 0\"><BR>\n" );
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