document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=128437>Question 128437</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A motorboat travels 120km upstream and then 120km downstream in a total of seven hours. If the speed of the river's current is 5km/h then what is the speed of the motorboat 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 #94027 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=94027\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A motorboat travels 120km upstream and then 120km downstream in a total of seven hours. If the speed of the river's current is 5km/h then what is the speed of the motorboat in still water.<BR>\n" );
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document.write( "Let s = boat speed in still water<BR>\n" );
document.write( "then<BR>\n" );
document.write( "(s+5) = boat speed downstream<BR>\n" );
document.write( "and<BR>\n" );
document.write( "(s-5) = boat speed up-stream<BR>\n" );
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document.write( "Write a time equation: Time = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=distance%2Fspeed ALIGN=MIDDLE  ALT=\"distance%2Fspeed\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "Time up + time down = 7 hrs<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=120%2F%28%28s-5%29%29 ALIGN=MIDDLE  ALT=\"120%2F%28%28s-5%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=120%2F%28%28s%2B5%29%29 ALIGN=MIDDLE  ALT=\"120%2F%28%28s%2B5%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 7<BR>\n" );
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document.write( "Multiply equation by the common denominator: (s+5)(s-5), resulting in:<BR>\n" );
document.write( "120(s+5) + 120(s-5) = 7(s-5)(s+5)<BR>\n" );
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document.write( "multiply what's inside the brackets<BR>\n" );
document.write( "120s + 600 + 120s - 600 = 7(s^2 - 25)<BR>\n" );
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document.write( "240s = 7s^2 - 175<BR>\n" );
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document.write( "0 = 7s^2 - 240s - 175; a quadratic equation<BR>\n" );
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document.write( "This will factor to:<BR>\n" );
document.write( "(7s + 5 )(s - 35) = 0<BR>\n" );
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document.write( "Positive solution:<BR>\n" );
document.write( "s = +35 km/hr is boat speed in still water<BR>\n" );
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document.write( "Check solution using the time equation:<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=120%2F40 ALIGN=MIDDLE  ALT=\"120%2F40\"   DISABLED_style= \"max-width:90%; height:auto;\" > + <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=120%2F30 ALIGN=MIDDLE  ALT=\"120%2F30\"   DISABLED_style= \"max-width:90%; height:auto;\" > =<BR>\n" );
document.write( "  3  +  4  = 7 hrs\r<BR>\n" );
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document.write( " </SPAN>\n" );
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