document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=263127>Question 263127</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The speed of a stream is 4 mph.  A boat travels 7 miles upstream in the same time it takes to travel 15 miles downstream.  What is the speed of the boat in still water?<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #193875 by </B><A HREF=/tutors/aboutme.mpl?userid=drk><B>drk(1908)</B></A><img src=\"/images/stars/stars-12.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=drk><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=193875\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> This is an RTD question. Here is a table based on the given information:<BR>\n" );
document.write( "up/down . . . . . . . . . . .rate . . . . . . . . . . .time . . . . . . . . . .distnace<BR>\n" );
document.write( "upstream . . . . . . . . . . r-4  . . . . . . . . . . T . . . . . . . . . . . . . . 7<BR>\n" );
document.write( "downstream . . . . . . . . r+4 . . . . . . . . . . T . . . . . . . . . . . . . . .15 <BR>\n" );
document.write( "Now, rate x time = distance, so<BR>\n" );
document.write( "time = distance / rate.<BR>\n" );
document.write( "solve each for T and we get<BR>\n" );
document.write( "T = (7/(r-4))<BR>\n" );
document.write( "T = (15/(r+4))<BR>\n" );
document.write( "set the times equal and we get<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7%2F%28r-4%29+=+15%2F%28r%2B4%29 ALIGN=MIDDLE  ALT=\"7%2F%28r-4%29+=+15%2F%28r%2B4%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "cross multiply to get<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7r+%2B+28+=+15r+-+60 ALIGN=MIDDLE  ALT=\"7r+%2B+28+=+15r+-+60\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "subtract 7r to get<BR>\n" );
document.write( " <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=28+=+8r+-+60 ALIGN=MIDDLE  ALT=\"28+=+8r+-+60\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "add 60 to both sides to get<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=88+=+8r ALIGN=MIDDLE  ALT=\"88+=+8r\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "divide by 8 to get<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r+=+8 ALIGN=MIDDLE  ALT=\"r+=+8\"   DISABLED_style= \"max-width:90%; height:auto;\" > </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );