document.write( "Question 708548: a boat traveled downstream a distance of 45 mi ad then came right back. if the speed of the stream was 12 mph and the total trip took 5 hours, find the average speed of the boat relative to the water \n" ); document.write( "
Algebra.Com's Answer #436137 by lwsshak3(11628)\"\" \"About 
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a boat traveled downstream a distance of 45 mi ad then came right back. if the speed of the stream was 12 mph and the total trip took 5 hours, find the average speed of the boat relative to the water
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\n" ); document.write( "let x= speed of boat in still water
\n" ); document.write( "x+12= speed of boat in downstream
\n" ); document.write( "x-12= speed of boat in upstream
\n" ); document.write( "..
\n" ); document.write( "travel time=distance/speed
\n" ); document.write( "45/(x+12)+45/(x-12)=5
\n" ); document.write( "45(x-12)+45(x+12)=5(x+12)(x-12)
\n" ); document.write( "45(x-12+x+12)=5(x^2-144)
\n" ); document.write( "90x=5x^2-720
\n" ); document.write( "5x^2-90x-720=0
\n" ); document.write( "x^2-18x-144=0
\n" ); document.write( "(x+6)(x-24)=0
\n" ); document.write( "x=-6 (reject, x>0)
\n" ); document.write( "x=24
\n" ); document.write( "average speed of the boat relative to the water: speed of boat twice the speed of the water
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