document.write( "Question 153972: The Hudson River flows at a rate of 3 miles per hour. A patrol boat travels 60 miles upriver, and returns in a total time of 9 hours. What is the speed of the boat in still water?
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Algebra.Com's Answer #113342 by checkley77(12844) $\"\"$ $\"About$

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distance=rate*time
\n" ); document.write( "d=rt
\n" ); document.write( "d/r=t
\n" ); document.write( "60/(r-3)+60/(r+3)=9
\n" ); document.write( "[60(r+3)+60(r-3)]/(r-3)(r+3)=9
\n" ); document.write( "60r+180+60r-180=9(r-3)(r+3)
\n" ); document.write( "120r=9(r^2-9)
\n" ); document.write( "120r=9r^2-81
\n" ); document.write( "9r^2-120r-81=0
\n" ); document.write( " $\"r=%28-b%2B-sqrt%28b%5E2-4%2Aa%2Ac%29%29%2F%282%2Aa%29\"$
\n" ); document.write( "r=(120+-sqrt[-120^2-4*9*-81])/2*9
\n" ); document.write( "r=(120+-sqrt[14,400+2,916])/18
\n" ); document.write( "r=(120+-sqrt17,316)/18
\n" ); document.write( "r=(120+-131.59)/18
\n" ); document.write( "r=(120+131.59)/18
\n" ); document.write( "r=251.59/18
\n" ); document.write( "r=13.98 mph for the speed of the boat.
\n" ); document.write( "proof:
\n" ); document.write( "60/(13.98-3)+60/13.98+3)=9
\n" ); document.write( "60/10.98+60/16.98=9
\n" ); document.write( "5.4645+3.5335=9
\n" ); document.write( "9~9
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