document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=910315>Question 910315</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat can travel 60 km/h in calm water.  The boat travels 200 km against the current and then returns to the location where it started.  If the trip takes 10 total hours, what is the speed of the current?\r<BR>\n" );
document.write( "\n" );
document.write( "I started with t = dr to r = t/d<BR>\n" );
document.write( "(1/60) x 10 = 10/600<BR>\n" );
document.write( "10/200 = 10/600<BR>\n" );
document.write( "cross multiply = 6000/2000=3<BR>\n" );
document.write( "I don't know if 3 would be the answer or if I have to do more, or if its the answer I don't know if its the right answer.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #552426 by </B><A HREF=/tutors/aboutme.mpl?userid=rothauserc><B>rothauserc(4718)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rothauserc><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=rothauserc><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=552426\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> rate(r) * time(t) = distance(d)<BR>\n" );
document.write( "let r be the speed of the current and t1 + t2 = 10 and d = 200, then<BR>\n" );
document.write( "let t1 be time with current and t2 time against current, then we have<BR>\n" );
document.write( "t1 + t2 = 10<BR>\n" );
document.write( "time with current is<BR>\n" );
document.write( "t1 = 200 / (60+r)<BR>\n" );
document.write( "time against current is<BR>\n" );
document.write( "t2 = 200 / (60-r)<BR>\n" );
document.write( "now we can add the two times<BR>\n" );
document.write( "200/(60+r) + 200/(60-r) = 10<BR>\n" );
document.write( "our lowest common denominator is (60+r)*(60-r)<BR>\n" );
document.write( "200*(60-r) + 200*(60+r) = 10 * (60+r) * (60-r)<BR>\n" );
document.write( "we can divide both sides of = by 10<BR>\n" );
document.write( "20*(60-r) + 20*(60+r) = 3600 - r^2<BR>\n" );
document.write( "simplify and combine like terms<BR>\n" );
document.write( "1200 -20r + 1200 +20r = 3600 - r^2<BR>\n" );
document.write( "2400 = 3600 -r^2<BR>\n" );
document.write( "r^2 = 1200<BR>\n" );
document.write( "r = square root of (1200) = 34.6 mph<BR>\n" );
document.write( "speed of current is 34.6 mph\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );