document.write( "Question 468233: A boat traveled downstream a distance of 45 miles and then came right back. If the speed of the current was 20 mph and the total trip took 3 hours, find the average speed of the boat relative to the water. \n" ); document.write( "
Algebra.Com's Answer #321269 by mananth(16946)\"\" \"About 
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Boat speed x
\n" ); document.write( "current speed 20
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\n" ); document.write( "against current x-20 mph
\n" ); document.write( "with current x+ 20 mph
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\n" ); document.write( "Distance= 45 miles
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\n" ); document.write( "Time against + time with = 3 hours\r
\n" ); document.write( "\n" ); document.write( "45/(x+20)+45/(x-20)=3
\n" ); document.write( "LCD = (x-20)(x+20)
\n" ); document.write( "45*(x-20)+45(x+20)= 3
\n" ); document.write( "45x-900+45x+900 =3(x ^2 -400)
\n" ); document.write( "90x=3x ^2-1200
\n" ); document.write( "3x^2-90 x-1200
\n" ); document.write( "Find the roots of the equation by quadratic formula
\n" ); document.write( "a= 3 , b= -90 , c= -1200
\n" ); document.write( "b^2-4ac=8100+ 14400
\n" ); document.write( "b^2-4ac=22500
\n" ); document.write( "\"sqrt%2822500%29=150%09\"
\n" ); document.write( "\"x=%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29\"
\n" ); document.write( "\"x1=%28-b%2Bsqrt%28b%5E2-4ac%29%29%2F%282a%29\"
\n" ); document.write( "x1=(90+150)/6
\n" ); document.write( "x1= 40
\n" ); document.write( "x2=( 90 -150 ) / 6
\n" ); document.write( "x2= -10
\n" ); document.write( "Ignore negative value
\n" ); document.write( "Speed of boat = 40 mph
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