document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1208940>Question 1208940</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A motorboat can maintain a constant speed of 16 miles per hour relative to the water. The boat makes a trip upstream to a certain point 20 minutes; the return trip take 15 minutes. What is the speed of the current? \r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #847482 by </B><A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><B>math_tutor2020(3816)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><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=847482\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=black size=3><BR>\n" );
document.write( "c = speed of the current in mph\r<BR>\n" );
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document.write( "Going against the current (i.e. upstream) the boat's speed goes from 16 mph to 16-c mph.<BR>\n" );
document.write( "distance = rate*time<BR>\n" );
document.write( "d = r*t<BR>\n" );
document.write( "d = (16-c)*(20/60)<BR>\n" );
document.write( "d = (1/3)(16-c)\r<BR>\n" );
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document.write( "Going with the current (downstream) means the boat goes from 16 mph to 16+c mph.<BR>\n" );
document.write( "d = r*t<BR>\n" );
document.write( "d = (16+c)*(15/60)<BR>\n" );
document.write( "d = (1/4)(16+c)\r<BR>\n" );
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document.write( "The two equations involve the same distance. <BR>\n" );
document.write( "This allows us to equate the right hand sides to solve for c.<BR>\n" );
document.write( "(1/3)(16-c) = (1/4)(16+c)<BR>\n" );
document.write( "12*(1/3)(16-c) = 12*(1/4)(16+c)<BR>\n" );
document.write( "4(16-c) = 3(16+c)<BR>\n" );
document.write( "64-4c = 48+3c<BR>\n" );
document.write( "64-48 = 3c+4c<BR>\n" );
document.write( "16 = 7c<BR>\n" );
document.write( "c = 16/7<BR>\n" );
document.write( "c = 2.2857 mph approximately\r<BR>\n" );
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document.write( "Side notes: <ul><li>To convert from mph to miles per minute, divide by 60.</li><li>The improper fraction 16/7 converts to the mixed number 2 & 2/7</li></ul></font> </SPAN>\n" );
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