document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=109824>Question 109824</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A boat can go 10 miles against the current in the same it can go in 30 miles with the current. The current flows at 4 mph. Find the speed of the boat in no current. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #80097 by </B><A HREF=/tutors/aboutme.mpl?userid=ptaylor><B>ptaylor(2198)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ptaylor><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=ptaylor><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=80097\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let r=rate (speed) of the boat with no current<BR>\n" );
document.write( "Now we know that:<BR>\n" );
document.write( "(r-4)=rate against the current<BR>\n" );
document.write( "(r+4)=rate with the current\r<BR>\n" );
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document.write( "distance(d)=rate(r) times time(t) or d=rt; t=d/r and r=d/t \r<BR>\n" );
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document.write( "Time required to go 10 miles against the current=10/(r-4)<BR>\n" );
document.write( "Time to go 30 miles with the current=30/(r+4)\r<BR>\n" );
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document.write( "----And we are told that the above two times are equal.  So our equation to solve:\r<BR>\n" );
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document.write( "10/(r-4)=30/(r+4)  multiply both sides by (r-4)(r+4) or cross-multiply and we get:\r<BR>\n" );
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document.write( "10(r+4)=30(r-4)  get rid of parens (distributive law)<BR>\n" );
document.write( "10r+40=30r-120 subtract 10r from and add 120 to both sides\r<BR>\n" );
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document.write( "10r-10r+40+120=30r-10r-120+120  collect like terms\r<BR>\n" );
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document.write( "160=20r  divide both sides by 20<BR>\n" );
document.write( "r=8 mph-------------------------------boat's rate of speed with no current\r<BR>\n" );
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document.write( "CK<BR>\n" );
document.write( "10/(8-4)=30/(8+4)<BR>\n" );
document.write( "10/4=30/12<BR>\n" );
document.write( "10/4=10/4\r<BR>\n" );
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document.write( "Hope this helps---ptaylor </SPAN>\n" );
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