document.write( "Question 886481: The rate of a river's current is 2 mph. A rowing crew can row 10mi down the river and back in 4 hours. Find the rowing rate in calm water. \n" ); document.write( "
Algebra.Com's Answer #535933 by lwsshak3(11628)\"\" \"About 
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The rate of a river's current is 2 mph. A rowing crew can row 10mi down the river and back in 4 hours. Find the rowing rate in calm water.
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\n" ); document.write( "let x=rate of rowoat in calm waters
\n" ); document.write( "x+2=rate of rowboat downstream
\n" ); document.write( "x-2=rate of rowboat upstream
\n" ); document.write( "travel time =distance/rate
\n" ); document.write( "\"10%2F%28x%2B2%29%2B10%2F%28x-2%29=4\"
\n" ); document.write( "lcd:(x+2)(x-2)
\n" ); document.write( "10(x-2)+10(x+2)=4(x+2)(x-2)
\n" ); document.write( "10x-20+10x+20=4(x^2-4)
\n" ); document.write( "20x=4x^2-16
\n" ); document.write( "4x^2-20x-16=0
\n" ); document.write( "x^2-5x-4=00.70
\n" ); document.write( "solve for x by quadratic formula
\n" ); document.write( "\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"
\n" ); document.write( "a=2, b=-20, c=2
\n" ); document.write( "ans:
\n" ); document.write( "x≈-0.70 (reject)
\n" ); document.write( "or
\n" ); document.write( "x≈5.7
\n" ); document.write( "rowing rate in calm water≈5.7 mph\r
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