document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=173348>Question 173348</A>This question is from textbook <A HREF=http://www.amazon.com/exec/obidos/ASIN/0321269470/algebrahomeworkh></A><BR>\n" );
document.write( ": <I><SPAN STYLE=\"word-break: break-all;\"> I have a word problem but I am stuck.\r<BR>\n" );
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document.write( "the current in a stream moves at a speed of 3mph.  A boat travels 45 mi upstream and 45 mi downstream in a total time of 8 hours.  What is the speed of the boat in still water?\r<BR>\n" );
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document.write( "45/r-3 + 45/r+3 = 8<BR>\n" );
document.write( "45(r+3) + 45(r-3)= 8(r+3)(r-3)<BR>\n" );
document.write( "90r = 8r^2 - 72<BR>\n" );
document.write( "and I'm stuck </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #128196 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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=128196\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> the current in a stream moves at a speed of 3mph. A boat travels 45 mi upstream and 45 mi downstream in a total time of 8 hours. What is the speed of the boat in still water? <BR>\n" );
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document.write( "Upstream DATA:<BR>\n" );
document.write( "distance  45 miles; rate = b-3 mph ; time = 45/(b-3)<BR>\n" );
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document.write( "Downstream DATA:<BR>\n" );
document.write( "distance = 45 miles ; rate = b+3 mph ; time = 45/(b+3)<BR>\n" );
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document.write( "time + time = 8 hrs.<BR>\n" );
document.write( "45/(b-3) + 45/(b+3) = 8<BR>\n" );
document.write( "45(b+3) + 45(b-3) = 8(b^2-9)<BR>\n" );
document.write( "90b = 8b^2-72<BR>\n" );
document.write( "8b^2-90b-72 = 0<BR>\n" );
document.write( "Use the quadratic formula whenever you cannot see the factors:<BR>\n" );
document.write( "b = [90 +- sqrt(8100 - 4*8*-72)]/16<BR>\n" );
document.write( "b = [90 +- sqrt(10404)]/16<BR>\n" );
document.write( "b = [90 +-102]/16<BR>\n" );
document.write( "Positive solution:<BR>\n" );
document.write( "b = 192/16 = 12 mph (speed of the boat in still water)<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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