document.write( "Question 587071: a girl flew her plane for 6 hr at a constant speed. She traveled 810 mi with the wind, then turned around and traveled 720 mi against the wind. The wind speed was a constant 15mph. Find the speed of the plane \n" ); document.write( "
Algebra.Com's Answer #373973 by lwsshak3(11628)\"\" \"About 
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a girl flew her plane for 6 hr at a constant speed. She traveled 810 mi with the wind, then turned around and traveled 720 mi against the wind. The wind speed was a constant 15mph. Find the speed of the plane.
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\n" ); document.write( "let x=speed of plane
\n" ); document.write( "speed downwind=x+15
\n" ); document.write( "speed against the wind=x-15
\n" ); document.write( "travel time= distance/speed
\n" ); document.write( "..
\n" ); document.write( "810/(x+15)+720/(x-15)=6
\n" ); document.write( "LCD:(x+15)(x-15)
\n" ); document.write( "810(x-15)+720(x+15)=6(x+15)(x-15)=6(x^2-225)
\n" ); document.write( "810x-12150+720x+10800=6x^2-1350
\n" ); document.write( "1530x-1350=6x^2-1350
\n" ); document.write( "6x^2-1530x=0
\n" ); document.write( "x^2-255x=0
\n" ); document.write( "x(x-255)=0
\n" ); document.write( "x=0 (reject)
\n" ); document.write( "or
\n" ); document.write( "x=255 mph
\n" ); document.write( "ans:
\n" ); document.write( "speed of plane=255 mph \n" ); document.write( "
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