document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1159172>Question 1159172</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A river has a current speed of 5 miles per hour. A boat travels down river for 20 miles. It then makes the return trip up the river. If the return trip took 8 hours and 20 minutes longer than the trip down river, what is 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 #782169 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><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=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=782169\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "If r is the speed in mph of the boat in still water, then its upstream speed is r-5 and its downstream speed is r+5.<br><BR>\n" );
document.write( "upstream time: 20/(r-5)<BR>\n" );
document.write( "downstream time: 20/(r+5)<br><BR>\n" );
document.write( "The upstream time is 8 1/3 hours (25/3 hours) greater than the downstream time:<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=20%2F%28r-5%29+=+20%2F%28r%2B5%29%2B25%2F3 ALIGN=MIDDLE  ALT=\"20%2F%28r-5%29+=+20%2F%28r%2B5%29%2B25%2F3\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "Multiply everything by the least common denominator, 3(r-5)(r+5):<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=60%28r%2B5%29+=+60%28r-5%29%2B25%28r%5E2-25%29 ALIGN=MIDDLE  ALT=\"60%28r%2B5%29+=+60%28r-5%29%2B25%28r%5E2-25%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=60r%2B300+=+60r-300%2B25r%5E2-625 ALIGN=MIDDLE  ALT=\"60r%2B300+=+60r-300%2B25r%5E2-625\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1225+=+25r%5E2 ALIGN=MIDDLE  ALT=\"1225+=+25r%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r%5E2+=+49 ALIGN=MIDDLE  ALT=\"r%5E2+=+49\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r+=+7 ALIGN=MIDDLE  ALT=\"r+=+7\"   DISABLED_style= \"max-width:90%; height:auto;\" >  (clearly the r = -7 solution makes no sense...)<br><BR>\n" );
document.write( "ANSWER: The speed of the boat in still water is 7mph<br><BR>\n" );
document.write( "CHECK:<BR>\n" );
document.write( "upstream speed: 20/(7-5) = 20/2 = 10<BR>\n" );
document.write( "downstream speed: 20/(7+5) = 20/12 = 5/3 = 1 2/3<BR>\n" );
document.write( "10 - 1 2/3 = 8 1/3<br><BR>\n" );
document.write( " </SPAN>\n" );
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