document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1007220>Question 1007220</A>: <I><SPAN STYLE=\"word-break: break-all;\"> David rowed a boat upstream for three miles and then returned to point he started from. The entire journey took four hours. The speed of the stream is one mile per hour. Find David's speed in still water.<BR>\n" );
document.write( "David's speed in still water is <BR>\n" );
document.write( " miles per hour. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #623254 by </B><A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><B>ankor@dixie-net.com(22740)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><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=ankor@dixie-net.com><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=623254\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  David rowed a boat upstream for three miles and then returned to point he started from.<BR>\n" );
document.write( " The entire journey took four hours.<BR>\n" );
document.write( " The speed of the stream is one mile per hour.<BR>\n" );
document.write( " Find David's speed in still water.<BR>\n" );
document.write( " :<BR>\n" );
document.write( "let s = his speed in still water<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s-1) = effective speed upstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s+1) = effective speed downstream<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Write time equation; time = dist/speed<BR>\n" );
document.write( ":<BR>\n" );
document.write( "time up + time down = 4 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=3%2F%28s-1%29 ALIGN=MIDDLE  ALT=\"3%2F%28s-1%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=3%2F%28s%2B1%29 ALIGN=MIDDLE  ALT=\"3%2F%28s%2B1%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 4 <BR>\n" );
document.write( "multiply equation by (s-1)(s+1), cancel the denominators and you ave<BR>\n" );
document.write( "3(s+1) + 3(s-1) = 4s(s-1)(s+1)<BR>\n" );
document.write( "3s + 3 + 3s - 3 = 4(s^2 - 1)<BR>\n" );
document.write( "6s = 4s^2 - 4<BR>\n" );
document.write( "Combine to form a quadratic on the right<BR>\n" );
document.write( "0 = 4s^2 - 6s - 4<BR>\n" );
document.write( "Simplify, divide by 2<BR>\n" );
document.write( "2s^2 - 3s - 2 = 0<BR>\n" );
document.write( "Factors to<BR>\n" );
document.write( "(2s+1)(s-2) = 0<BR>\n" );
document.write( "The positive solution<BR>\n" );
document.write( "s = 2 mph in still water<BR>\n" );
document.write( ":<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Confirm this by finding the actual time each way, using the effective speeds<BR>\n" );
document.write( "3/1 = 3<BR>\n" );
document.write( "3/3 = 1<BR>\n" );
document.write( "------------<BR>\n" );
document.write( "total 4 hrs </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );