document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=375325>Question 375325</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat travels 80 miles upstream in a river with a current of 6 miles per hour; then it travels back down to its starting point.  The total time of the trip was 4 hours.  Find the speed of the boat in still water.  what is the equation too? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #266877 by </B><A HREF=/tutors/aboutme.mpl?userid=mananth><B>mananth(16946)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=mananth><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=mananth><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=266877\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> let speed of boat in still water be x mph<BR>\n" );
document.write( "..<BR>\n" );
document.write( "current speed = 6 mph.<BR>\n" );
document.write( "..<BR>\n" );
document.write( "speed upstream = x-6 mph<BR>\n" );
document.write( "speed downstream = x+6 mph.<BR>\n" );
document.write( "..<BR>\n" );
document.write( "t = d/r<BR>\n" );
document.write( "time upstream + time downstream = 4 hours<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=80%2F%28x-6%29%2B80%2F%28x%2B6%29+=4 ALIGN=MIDDLE  ALT=\"80%2F%28x-6%29%2B80%2F%28x%2B6%29+=4\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "..<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%2880%2A%28x%2B6%29%2B80%2A%28x-60%29%29%2F%28%28x%2B6%29%2A%28x-6%29%29=4 ALIGN=MIDDLE  ALT=\"%2880%2A%28x%2B6%29%2B80%2A%28x-60%29%29%2F%28%28x%2B6%29%2A%28x-6%29%29=4\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "...<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%2880x%2B480%2B80x-480%29%2F%28%28x%2B6%29%28x-6%29%29=4 ALIGN=MIDDLE  ALT=\"%2880x%2B480%2B80x-480%29%2F%28%28x%2B6%29%28x-6%29%29=4\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "...<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28160x%29%2F%28%28x%2B6%29%28x-6%29%29=4 ALIGN=MIDDLE  ALT=\"%28160x%29%2F%28%28x%2B6%29%28x-6%29%29=4\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "...<BR>\n" );
document.write( "multiply by (x+6)(x-6)<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28160x%29%2A%28cross%28%28x%2B6%29%28x-6%29%29%29%2F%28%28cross%28%28x%2B6%29%28x-6%29%29%29%29=4%28x%2B6%29%28x-6%29 ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "..<BR>\n" );
document.write( "160x= 4x^2-36<BR>\n" );
document.write( "4x^2-160x-36=0<BR>\n" );
document.write( "/4<BR>\n" );
document.write( "x^2-40x-9=0<BR>\n" );
document.write( "discriminant = 1636<BR>\n" );
document.write( "x1=((40+sqrt(1636)))/2<BR>\n" );
document.write( "x1=40.2 mph speed of boat in still water<BR>\n" );
document.write( "x2 will be negative so ignore<BR>\n" );
document.write( "...<BR>\n" );
document.write( "m.ananth@hotmail.ca </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );