document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=851788>Question 851788</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat travels 15km/hr in still water. In travelling 45 km downstream from Town A to Town B, it completes the journey in 75 minutes less than it takes for the return journey. At what speed does the river flow?<BR>\n" );
document.write( "Please explain simply. Apparently I am an idiot. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #512999 by </B><A HREF=/tutors/aboutme.mpl?userid=lwsshak3><B>lwsshak3(11628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=lwsshak3><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=512999\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A boat travels 15km/hr in still water. In travelling 45 km downstream from Town A to Town B, it completes the journey in 75 minutes less than it takes for the return journey. At what speed does the river flow?<BR>\n" );
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document.write( "let x=speed of river flow<BR>\n" );
document.write( "15+x=speed of boat downstream<BR>\n" );
document.write( "15-x=speed of boat upstream<BR>\n" );
document.write( "travel time=distance/speed<BR>\n" );
document.write( "...<BR>\n" );
document.write( "travel time upstream=45/(15-x) (return trip)<BR>\n" );
document.write( "travel time downstream=45/(15+x)<BR>\n" );
document.write( "75 min=(75/60) hr<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=45%2F%2815-x%29-45%2F%2815%2Bx%29=75%2F60 ALIGN=MIDDLE  ALT=\"45%2F%2815-x%29-45%2F%2815%2Bx%29=75%2F60\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "LCD:(15-x)(15+x)(60)<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=60%2A45%2815%2Bx%29-60%2A45%2815-x%29=75%2815-x%29%2815%2Bx%29 ALIGN=MIDDLE  ALT=\"60%2A45%2815%2Bx%29-60%2A45%2815-x%29=75%2815-x%29%2815%2Bx%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "40500+2700x-40500+2700x=75(225-x^2)<BR>\n" );
document.write( "5400x=16875-75x^2<BR>\n" );
document.write( "75x^2+5400x-16875=0<BR>\n" );
document.write( "divide by 75<BR>\n" );
document.write( "x^2+72-225=0<BR>\n" );
document.write( "solve for x by quadratic formula:<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ ALIGN=MIDDLE  ALT=\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "a=1, b=72, c=-225<BR>\n" );
document.write( "ans:<BR>\n" );
document.write( "x=-12.37 (reject)<BR>\n" );
document.write( "or<BR>\n" );
document.write( "x=12.37<BR>\n" );
document.write( "speed of river flow=12.37 km/hr\r<BR>\n" );
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