document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=455185>Question 455185</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 1o min. If the current in that part of the river is 3 km per hour, what was her boat speed in still water?\r<BR>\n" );
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document.write( "Can someone show me the set up for this? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #312530 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=312530\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 1o min. If the current in that part of the river is 3 km per hour, what was her boat speed in still water? <BR>\n" );
document.write( "Can someone show me the set up for this?<BR>\n" );
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document.write( "Upstream DATA:<BR>\n" );
document.write( "time = 1/2 hr ; distance = x km ; rate = d/t = x/(1/2) = (2x) km/h<BR>\n" );
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document.write( "Downstream DATA:<BR>\n" );
document.write( "time = 1/6 hr ; distance = x km ; rate = d/t = x/(1/6) = (6x) km/h<BR>\n" );
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document.write( "Upstream rate = b-3 km/h where b is the speed of the boat in still water<BR>\n" );
document.write( "Downstream rate b+3 km/h <BR>\n" );
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document.write( "Solve this system of equations:<BR>\n" );
document.write( "rate = rate:<BR>\n" );
document.write( "b-3 = (2x)<BR>\n" );
document.write( "b+3 = (6x)<BR>\n" );
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document.write( "Subtract and solve for \"x\":<BR>\n" );
document.write( "6 = 4x<BR>\n" );
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document.write( "x = 3/2 km<BR>\n" );
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document.write( "Solve for \"b\":<BR>\n" );
document.write( "b -3 = 2x<BR>\n" );
document.write( "b -3 = 2(3/2)<BR>\n" );
document.write( "b -3 = 3<BR>\n" );
document.write( "b = 6 km/h (speed of the boat in still water)<BR>\n" );
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document.write( "A shorter way to work the problem.<BR>\n" );
document.write( "Let b+3 be downstream rate.<BR>\n" );
document.write( "and b-3 be upstream rate.<BR>\n" );
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document.write( "Distance up = Distance down = (rate)(time)<BR>\n" );
document.write( "(b+3)(1/6 hr) = (b-3)(1/2 hr)<BR>\n" );
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document.write( "Multiply both sides by 12 to get:<BR>\n" );
document.write( "2b+6 = 6b-18<BR>\n" );
document.write( "4b = 24<BR>\n" );
document.write( "b = 6 km/hr (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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