document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=706308>Question 706308</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat, which moves at 18 miles per hour in water without a current, goes 80 miles upstream and 80 miles back again in 9 hours. Find the speed of the current to the nearest tenth.\r<BR>\n" );
document.write( "\n" );
document.write( "I am very confused on how to work out this problem... </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #435072 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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=435072\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A boat, which moves at 18 miles per hour in water without a current, goes 80 miles upstream and 80 miles back again in 9 hours. Find the speed of the current to the nearest tenth. <BR>\n" );
document.write( "----<BR>\n" );
document.write( "Let current speed be \"c\" .<BR>\n" );
document.write( "------------------------------------------------------<BR>\n" );
document.write( "Upstream DATA:<BR>\n" );
document.write( "distance = 80 miles ; rate = 18-c mph ; time = d/r = 80/(18-c) hrs.<BR>\n" );
document.write( "---------------------------------<BR>\n" );
document.write( "Downstream DATA:<BR>\n" );
document.write( "distance = 80 miles ; rate = 19+c mph ; time = d/r = 80/(18+c) hrs<BR>\n" );
document.write( "----------------------------------------<BR>\n" );
document.write( "Equation:<BR>\n" );
document.write( "time up + time down = 9 hrs<BR>\n" );
document.write( "80/(18-c) + 80/(18+c) = 9<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "80(18+c) + 80(18-c) = 9(18-c)(18+c)<BR>\n" );
document.write( "---------------------------------------------<BR>\n" );
document.write( "2*80*18 = 9(324-c^2)<BR>\n" );
document.write( "320 = 324-c^2<BR>\n" );
document.write( "c^2 = 4<BR>\n" );
document.write( "c = 2 mph (speed of the current)<BR>\n" );
document.write( "------------------------------------<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );