document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1066350>Question 1066350</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat traveled downstream a distance of 50 mi and then came right back. If the speed of the current was 20 mph and the total trip took 3 hours and 20 minutes, find the average speed of the boat relative to the water. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #681520 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=681520\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> speed of boat is x<BR>\n" );
document.write( "speed of current is 20 mph<BR>\n" );
document.write( "x+20* t1=50, so t1=50/(x+20)<BR>\n" );
document.write( "x-20*t2=50, so t2=50/(x-20)<BR>\n" );
document.write( "50/(x+20)+50/(x-20)=10/3, where 10/3 is hours.<BR>\n" );
document.write( "multiply everything by (x+20)(x-20 or x^2-400<BR>\n" );
document.write( "50(x-20)+50(x+20)=(10/3)x^2-4000/3; the left side is equal to 100x<BR>\n" );
document.write( "(10/3)x^2-100x-4000/3=0<BR>\n" );
document.write( "multiply everything by 3 then divide everything by 10.<BR>\n" );
document.write( "10x^2-300x-4000=0<BR>\n" );
document.write( "x^2-30x-400=0<BR>\n" );
document.write( "(x-40)(x+10)=0<BR>\n" );
document.write( "x=40 mph, only positive root ANSWER.<BR>\n" );
document.write( "goes 60 mph downstream and takes 5/6 hr or 50 minutes<BR>\n" );
document.write( "goes 20 mph upstream and takes 2.5 hours or 150 minutes.<BR>\n" );
document.write( "That takes 200 minutes, which is 3h20m </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );