document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=530140>Question 530140</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat takes 4 hours to travel 36 miles downstream and 12 hours for the return trip. What is the speed of the current and 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 #349910 by </B><A HREF=/tutors/aboutme.mpl?userid=KMST><B>KMST(5328)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=KMST><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=KMST><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=349910\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The apparent speed is 9mph with the current and 3 mph against the current.<BR>\n" );
document.write( "The average is the speed of the boat in still water (6mph) and the difference is the speed of the current (3mph).<BR>\n" );
document.write( "However, the intention of the problem must have been to set and solve a system of equations, so let's get silly.<BR>\n" );
document.write( "Let <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b ALIGN=MIDDLE  ALT=\"b\"   DISABLED_style= \"max-width:90%; height:auto;\" > be the speed of the boat in still water in mph, and<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r ALIGN=MIDDLE  ALT=\"r\"   DISABLED_style= \"max-width:90%; height:auto;\" > be the speed of the current in mph.<BR>\n" );
document.write( "We could say that the total speed going downstream, in mph, is<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b%2Br=9 ALIGN=MIDDLE  ALT=\"b%2Br=9\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "and that the total speed for the return trip, in mph, is<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b-r=3 ALIGN=MIDDLE  ALT=\"b-r=3\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "Then we solve the system of equations.<BR>\n" );
document.write( "We could do it by substitution, solving for <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b ALIGN=MIDDLE  ALT=\"b\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "in the second equation <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b=r%2B3 ALIGN=MIDDLE  ALT=\"b=r%2B3\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "and substituting that into the first equation to get<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28r%2B3%29%2B3=9 ALIGN=MIDDLE  ALT=\"%28r%2B3%29%2B3=9\"   DISABLED_style= \"max-width:90%; height:auto;\" > so <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r%2B6=9 ALIGN=MIDDLE  ALT=\"r%2B6=9\"   DISABLED_style= \"max-width:90%; height:auto;\" >, so <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r=9-6 ALIGN=MIDDLE  ALT=\"r=9-6\"   DISABLED_style= \"max-width:90%; height:auto;\" > so <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r=3 ALIGN=MIDDLE  ALT=\"r=3\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "Then we substitute that solution in<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b=r%2B3 ALIGN=MIDDLE  ALT=\"b=r%2B3\"   DISABLED_style= \"max-width:90%; height:auto;\" > and find <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b=3%2B3 ALIGN=MIDDLE  ALT=\"b=3%2B3\"   DISABLED_style= \"max-width:90%; height:auto;\" > so <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b=6 ALIGN=MIDDLE  ALT=\"b=6\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "We could also solve by other methods, but it's Friday night and I have other stuff to do. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );