document.write( "Question 964017: A plane flies 720 mi against a steady 30-mi/h head-wind and then returns to the same point with the wind. If the entire trip takes 10 hr, what is the plane's speed in still air? \n" ); document.write( "
Algebra.Com's Answer #588917 by lwsshak3(11628)\"\" \"About 
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A plane flies 720 mi against a steady 30-mi/h head-wind and then returns to the same point with the wind. If the entire trip takes 10 hr, what is the plane's speed in still air?
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\n" ); document.write( "let x=plane's speed in still air
\n" ); document.write( "(x+30)=plane's speed with the wind
\n" ); document.write( "(x-30)=plane's speed against the wind
\n" ); document.write( "travel time=distance/speed
\n" ); document.write( "\"720%2F%28x-30%29%2B720%2F%28x%2B30%29=10\"
\n" ); document.write( "lcd:(x+30)(x+30)=(x^2-900)
\n" ); document.write( "720x+21600+720x-21600=10(x^2-900)
\n" ); document.write( "1440x=10x^2-9000
\n" ); document.write( "10x^2-1440x-9000=0
\n" ); document.write( "x^2-144x-900=0
\n" ); document.write( "(x-150)(x+6)=0
\n" ); document.write( "x=150
\n" ); document.write( "what is the plane's speed in still air? 150 mph
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