document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=206290>Question 206290</A>: <I><SPAN STYLE=\"word-break: break-all;\"> the current in a river moves at 2mph. a boat travels 18 mph upstream and 7mph down stream in a total 7 hours. what the speed of the boat in still water? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #155890 by </B><A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><B>ankor@dixie-net.com(22740)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><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=ankor@dixie-net.com><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=155890\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> I assume when you say 18 mph you mean 18 miles, and 7 mph mean 7 miles.<BR>\n" );
document.write( ":<BR>\n" );
document.write( "the current in a river moves at 2mph. a boat travels 18 miles upstream<BR>\n" );
document.write( " and 7 miles down stream in a total 7 hours. <BR>\n" );
document.write( "what the speed of the boat in still water?<BR>\n" );
document.write( ";<BR>\n" );
document.write( "Let s = speed of the boat in still water<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s+2) = speed downstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s-2) = speed upstream<BR>\n" );
document.write( ";<BR>\n" );
document.write( "Write a time equation: Time = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=dist%2Fspeed ALIGN=MIDDLE  ALT=\"dist%2Fspeed\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "Time downstream + time upstream = 7 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=18%2F%28%28s%2B2%29%29 ALIGN=MIDDLE  ALT=\"18%2F%28%28s%2B2%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7%2F%28%28s-2%29%29 ALIGN=MIDDLE  ALT=\"7%2F%28%28s-2%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 7<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Multiply equation by (s+2)(s-2)<BR>\n" );
document.write( "(s+2)(s-2)*<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=18%2F%28%28s%2B2%29%29 ALIGN=MIDDLE  ALT=\"18%2F%28%28s%2B2%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + (s+2)(s-2)*<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7%2F%28%28s-2%29%29 ALIGN=MIDDLE  ALT=\"7%2F%28%28s-2%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 7*(s+2)(s-2)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Cancel the denominators and you have:<BR>\n" );
document.write( "18(s-2) + 7(s+2) = 7*(s^2 - 4)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "18s - 36 + 7s + 14 = 7s^2 - 28<BR>\n" );
document.write( ":<BR>\n" );
document.write( "25s - 22 = 7s^2 - 28<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Arrange as a quadratic equation on the right<BR>\n" );
document.write( "0 = 7s^2 - 25s - 28 + 22 <BR>\n" );
document.write( ":<BR>\n" );
document.write( "7s^2 - 25s - 6 = 0<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Use the quadratic formula to find s<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ ALIGN=MIDDLE  ALT=\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "In this problem x = s; a = 7; b = -25; c = -6<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=s+=+%28-%28-25%29+%2B-+sqrt%28-25%5E2+-+4+%2A+7+%2A+-6+%29%29%2F%282%2A7%29+ ALIGN=MIDDLE  ALT=\"s+=+%28-%28-25%29+%2B-+sqrt%28-25%5E2+-+4+%2A+7+%2A+-6+%29%29%2F%282%2A7%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=s+=+%2825+%2B-+sqrt%28625+-+%28-168%29+%29%29%2F14+ ALIGN=MIDDLE  ALT=\"s+=+%2825+%2B-+sqrt%28625+-+%28-168%29+%29%29%2F14+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=s+=+%2825+%2B-+sqrt%28625+%2B+168+%29%29%2F14+ ALIGN=MIDDLE  ALT=\"s+=+%2825+%2B-+sqrt%28625+%2B+168+%29%29%2F14+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=s+=+%2825+%2B-+sqrt%28793+%29%29%2F14+ ALIGN=MIDDLE  ALT=\"s+=+%2825+%2B-+sqrt%28793+%29%29%2F14+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "The positive solution is what we want here<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=s+=+%2825+%2B+28.16%29%2F14+ ALIGN=MIDDLE  ALT=\"s+=+%2825+%2B+28.16%29%2F14+\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "s = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=53.16%2F14 ALIGN=MIDDLE  ALT=\"53.16%2F14\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "s ~ 3.8 mph in still water<BR>\n" );
document.write( ":<BR>\n" );
document.write( ":<BR>\n" );
document.write( "That is awful slow, let's see if that's true<BR>\n" );
document.write( "Upstream time + downstream time =<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7%2F1.8 ALIGN=MIDDLE  ALT=\"7%2F1.8\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=18%2F5.8 ALIGN=MIDDLE  ALT=\"18%2F5.8\"   DISABLED_style= \"max-width:90%; height:auto;\" > =<BR>\n" );
document.write( "3.89 + 3.10 = 6.99 ~ 7 hrs<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );