document.write( "Question 889087: A man travels 40km down a river and back in 6 hours. If the speed of river current is 5km/hr, find speed of boat in still water. \n" ); document.write( "

Algebra.Com's Answer #537883 by lwsshak3(11628) $\"\"$ $\"About$

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A man travels 40km down a river and back in 6 hours. If the speed of river current is 5km/hr, find speed of boat in still water.
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\n" ); document.write( "let x=speed of boat in still water
\n" ); document.write( "x+5=speed of boat in down river
\n" ); document.write( "x-5=speed of boat in up river
\n" ); document.write( "travel time=distance/speed
\n" ); document.write( "..
\n" ); document.write( " $\"40%2F%28x%2B5%29%2B40%2F%28x-5%29=6\"$
\n" ); document.write( "lcd:(x+5)(x-5)
\n" ); document.write( "40(x-5)+40(x+5)=6(x^2-25)
\n" ); document.write( "40x-200+40x+200=6x^2-150
\n" ); document.write( "6x^2-80x-150=0
\n" ); document.write( "3x^2-40x-75=0
\n" ); document.write( "(3x+5)(x-15)=0
\n" ); document.write( "x=-5/3 (reject)
\n" ); document.write( "or
\n" ); document.write( "x=15
\n" ); document.write( "speed of boat in still water=15 mph
\n" ); document.write( " \n" ); document.write( "

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