document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1056878>Question 1056878</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A small motorboat travels 15 mph in still water. It takes 1 hour longer to travel 72 miles going upstream than it does going downstream. Find the speed of the current. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #671943 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=671943\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> velocity* time=distance<BR>\n" );
document.write( "upstream is 15-x<BR>\n" );
document.write( "downstream is 15+x, where x is the current speed.<BR>\n" );
document.write( "15+x*time1=72<BR>\n" );
document.write( "time1=72/(15+x)<BR>\n" );
document.write( "15-x*time2=72<BR>\n" );
document.write( "time2=72/(15-x)<BR>\n" );
document.write( "time 2 is 1 more than time 1<BR>\n" );
document.write( "so 72/(15-x)-1=72/(15+x)<BR>\n" );
document.write( "Multiply everything by (15+x)(15-x) to clear fractions<BR>\n" );
document.write( "72(15+x)-(225-x^2)=72(15-x)<BR>\n" );
document.write( "1080+72x-225+x^2=1080-72x.  The 1080 cancel<BR>\n" );
document.write( "x^2+144x-225=0<BR>\n" );
document.write( "x=(1/2)(-144+ sqrt (20736+900);sqrt (21636)=147.09; x=(1/2)3.09, using only the positive root.<BR>\n" );
document.write( "x=1.545 mph current. ANSWER<BR>\n" );
document.write( "Upstream is 13.455 mph and it takes 5.35 hours<BR>\n" );
document.write( "Downstream is 16.545 mph and it takes 4.35 hours </SPAN>\n" );
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