document.write( "Question 180565: The Hudson River flows at a rate of 5 miles per hour. A patrol boat travels 40 miles upriver and returns in a total time of 6 hours. What's the speed of the boat in still water? \n" ); document.write( "

Algebra.Com's Answer #135349 by HyperBrain(694) $\"\"$ $\"About$

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Let r=rate of boat in still water
\n" ); document.write( "Then r-5=rate of boat upstream
\n" ); document.write( "

r+5=rate of boat downstream\r
\n" ); document.write( "\n" ); document.write( " $\"40%2F%28r-5%29%2B40%2F%28r%2B5%29=6\"$
\n" ); document.write( "40(r+5)+40(r-5)=6(r²-25)
\n" ); document.write( "40(2r)=80r=6r²-150
\n" ); document.write( "6r²-80r-150=0
\n" ); document.write( "3r²-40r-75=0
\n" ); document.write( "(r-15)(3r+5)=0
\n" ); document.write( "r-15=0
\n" ); document.write( "r=15
\n" ); document.write( "3r+5=0
\n" ); document.write( "r=-5/3>>Not valid since the rate of the boat must be positive.\r
\n" ); document.write( "\n" ); document.write( "Therefore, the boat travels 15 mi/hr in still water.\r
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