document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=557452>Question 557452</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Clark has a boat that can travel at 15kph in still water. It can go 140km with the current at the same time it takes to travel 35km against the current.<BR>\n" );
document.write( "what is the speed of the river?? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #362614 by </B><A HREF=/tutors/aboutme.mpl?userid=oberobic><B>oberobic(2304)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=oberobic><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=362614\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Always start with the basic distance equation:  d = r*t, where d=distance, r=rate (or speed), and t=time.<BR>\n" );
document.write( "s = speed in still water = 15 km/hr<BR>\n" );
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document.write( "The current in the river may be defined as 'c'.<BR>\n" );
document.write( "Going against the current, r = s-c, which means the current slows the boat down.<BR>\n" );
document.write( "Going with the current, r = s+c, which means the current speeds the boat along.<BR>\n" );
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document.write( "Going upstream (that is, against the current), the boat goes 15 km.<BR>\n" );
document.write( "Going downstream  (that is, with the current), the boat goes 140 km.<BR>\n" );
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document.write( "These distances are covered in the same time.<BR>\n" );
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document.write( "d = r*t<BR>\n" );
document.write( "so<BR>\n" );
document.write( "t= d/r<BR>\n" );
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document.write( "140 = (s+c) * t = (15+c)*t<BR>\n" );
document.write( "35 = (s-c) * t = (15-c)*t<BR>\n" );
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document.write( "140/(15+c) = t<BR>\n" );
document.write( "35/(15-c) = t<BR>\n" );
document.write( "t = t<BR>\n" );
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document.write( "140/(15+c) = 35/(15-c)<BR>\n" );
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document.write( "cross multiply<BR>\n" );
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document.write( "140*(15-c) = 35*(15+c)<BR>\n" );
document.write( "2100 - 140c = 525 + 35c<BR>\n" );
document.write( "1575 = 175c<BR>\n" );
document.write( "c = 1575/175<BR>\n" );
document.write( "c = 9<BR>\n" );
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document.write( "check this answer<BR>\n" );
document.write( "t = 140/(15+9) = 140/24 = 35/6<BR>\n" );
document.write( "t = 35/(15-9) = 35/6<BR>\n" );
document.write( "t = t<BR>\n" );
document.write( "correct<BR>\n" );
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document.write( "Answer:  The river's current is 9 km/hr.<BR>\n" );
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document.write( "Done. </SPAN>\n" );
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