document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=22105>Question 22105</A>: <I><SPAN STYLE=\"word-break: break-all;\"> River flows at 2 mph.  Phil can paddle in still water at 8 mph.  If he is 4 miles downstream from a log floating toward him, <BR>\n" );
document.write( "how long will it take him to reach the log? </SPAN>\n" );
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document.write( "Answer: <font color=red>1/2 of an hour</font> or <font color=red>30 minutes</font>\r<BR>\n" );
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document.write( "Explanation\r<BR>\n" );
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document.write( "Let's say the river flows south.<BR>\n" );
document.write( "Define points A, B, and C such that:<BR>\n" );
document.write( "A = log's starting location<BR>\n" );
document.write( "B = Phil's starting location<BR>\n" );
document.write( "C = point in between A and B where Phil reaches the log<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%0D%0Adrawing%28300%2C300%2C-10%2C10%2C-10%2C10%2C%0D%0Aline%280%2C5%2C0%2C-7%29%2C%0D%0Acircle%280%2C3%2C0.2%29%2Ccircle%280%2C3%2C0.25%29%2Ccircle%280%2C3%2C0.3%29%2C%0D%0Acircle%280%2C-1%2C0.2%29%2Ccircle%280%2C-1%2C0.25%29%2Ccircle%280%2C-1%2C0.3%29%2C%0D%0Acircle%280%2C-4%2C0.2%29%2Ccircle%280%2C-4%2C0.25%29%2Ccircle%280%2C-4%2C0.3%29%2C%0D%0A%0D%0Aline%284%2C2%2C4%2C-5%29%2Cline%284%2C-5%2C3.65%2C-4.3938%29%2Cline%284.05%2C-5%2C4.4%2C-4.3938%29%2C%0D%0A%0D%0Alocate%280.4%2C4.2%2C%22A%22%29%2C%0D%0Alocate%280.4%2C-1.8%2B0.8%2C%22C%22%29%2C%0D%0Alocate%280.4%2B0.1%2C-3.8%2C%22B%22%29%2C%0D%0Alocate%284.5%2C0%2Cmatrix%281%2C2%2C%22river%22%2C%22flow%22%29%29%2C%0D%0Alocate%28-9%2C-9%2Cmatrix%281%2C4%2C%22Diagram%22%2C%22not%22%2C%22to%22%2C%22scale%22%29%29%0D%0A%29%0D%0A ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "The diagram is optional but could be handy.\r<BR>\n" );
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document.write( "Phil's speed is 8 mph in still water.<BR>\n" );
document.write( "But since Phil has to swim upstream against the 2 mph current, it slows him down to 8-2 = 6 mph.<BR>\n" );
document.write( "So he travels 6x miles where x is the length of time in hours.<BR>\n" );
document.write( "I'm using the formula: <PRE STYLE=\"white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;\">distance = rate*time</PRE>Meanwhile, the log travels at 2 mph for the same amount of time x.<BR>\n" );
document.write( "It travels 2x miles.\r<BR>\n" );
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document.write( "To recap so far we have these distances<BR>\n" );
document.write( "AC = 2x<BR>\n" );
document.write( "BC = 6x\r<BR>\n" );
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document.write( "These two distance subtotals must add to the 4 mile gap between the points A and B.<BR>\n" );
document.write( "AC+BC = AB<BR>\n" );
document.write( "2x+6x = AB<BR>\n" );
document.write( "2x+6x = 4<BR>\n" );
document.write( "8x = 4<BR>\n" );
document.write( "x = 4/8<BR>\n" );
document.write( "x = <font color=red>1/2 of an hour</font> aka <font color=red>30 minutes</font><BR>\n" );
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