document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=511374>Question 511374</A>: <I><SPAN STYLE=\"word-break: break-all;\"> hi can someone help me with this..\r<BR>\n" );
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document.write( "A man can row 12 miles upstream in a river and back in 7 1/2 hours. He can row 1 mile upstream in th same time that he can row 4 miles downstream. Find the speed of the boat in still water and the speed of the current. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #342184 by </B><A HREF=/tutors/aboutme.mpl?userid=lwsshak3><B>lwsshak3(11628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=lwsshak3><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=342184\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A man can row 12 miles upstream in a river and back in 7 1/2 hours. He can row 1 mile upstream in th same time that he can row 4 miles downstream. Find the speed of the boat in still water and the speed of the current.<BR>\n" );
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document.write( "2 conditions given, so use 2 equations to solve:\r<BR>\n" );
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document.write( "let x=speed of boat in still water<BR>\n" );
document.write( "let c=speed of current<BR>\n" );
document.write( "x+c =speed of boat downstream<BR>\n" );
document.write( "x-c = speed of boat upstream<BR>\n" );
document.write( "..<BR>\n" );
document.write( "Travel time=distance/speed<BR>\n" );
document.write( "1/(x-c)=4/(x+c)<BR>\n" );
document.write( "x+c=4x-4c<BR>\n" );
document.write( "5c=3x<BR>\n" );
document.write( "c=3x/5<BR>\n" );
document.write( "..<BR>\n" );
document.write( "12/(x-c)+12/(x+c)=7.5<BR>\n" );
document.write( "LCD:(x+c)(x-c)<BR>\n" );
document.write( "12x+12c+12x-12c=7.5(x+c)(x-c)<BR>\n" );
document.write( "24x=7.5(x^2-c^2) (difference of squares)<BR>\n" );
document.write( "24x=7.5(x^2-(3x/5)^2)=7.5(x^2-9x^2/25)=7.5[(25x^2-9x^2)/25]<BR>\n" );
document.write( "24x=7.5[16x^2/25]=(7.5/25)(16x^2)=.3(16x^2)=4.8x^2<BR>\n" );
document.write( "4.8x^2-24x=0<BR>\n" );
document.write( "x(4.8x-24=0<BR>\n" );
document.write( "x=0 (reject, speed>0)<BR>\n" );
document.write( "4.8x-24=0<BR>\n" );
document.write( "x=24/4.8=5 mph<BR>\n" );
document.write( "c=3x/5=15/5=3mph<BR>\n" );
document.write( "ans:<BR>\n" );
document.write( "speed of boat in still water=5 mph<BR>\n" );
document.write( "speed of current=3 mph </SPAN>\n" );
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