document.write( "Question 872087: The current river flows at the rate of 4mph. In order for a boat to travel 24 miles up river and then return I'm a total of 5 hours how fast must the boat be able to travel in still water? \n" ); document.write( "
Algebra.Com's Answer #525944 by lwsshak3(11628)\"\" \"About 
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The current river flows at the rate of 4mph. In order for a boat to travel 24 miles up river and then return in a total of 5 hours how fast must the boat be able to travel in still water?
\n" ); document.write( "***
\n" ); document.write( "let x=speed of boat in still water
\n" ); document.write( "x+4=speed of boat downstream
\n" ); document.write( "x-4=speed of boat upstream
\n" ); document.write( "travel time=distance/speed
\n" ); document.write( "..
\n" ); document.write( "24/(x+4)+24/(x-4)=5
\n" ); document.write( "24(x-4)+24(x+4)=5(x+4)(x-4)
\n" ); document.write( "24x-96+24x+96=5(x^2-16)
\n" ); document.write( "48x=5x^2-80
\n" ); document.write( "5x^2-48x-80=0
\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=5, b=-48, c=-80
\n" ); document.write( "ans:
\n" ); document.write( "x≈-1.45(reject)
\n" ); document.write( "or
\n" ); document.write( "x≈11.05
\n" ); document.write( "speed of boat in still water≈ 11.05 mph \n" ); document.write( "
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