document.write( "Question 96041This question is from textbook Beginning Algebra
\n" ); document.write( ": I need help with this problem.\r
\n" ); document.write( "\n" ); document.write( "A plane flies 720 mi against a steady 30 mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane's speed in still air?\r
\n" ); document.write( "\n" ); document.write( "Here is what I know: If r is the rate of the plane (in miles per hour)in still air, then the rate against the wind would be r - 30 and the rate with the wind would be r + 30. I don't know what to do after this point. \n" ); document.write( "
Algebra.Com's Answer #69942 by checkley71(8403)\"\" \"About 
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720/(X-30)+720/(X+30)=10
\n" ); document.write( "[720(X+30)+720(X-30)]/(X-30)(X+30)=10
\n" ); document.write( "(720X+21600+720X-21600)/X^2-900=10 NOW CROSS MULTIPLY:
\n" ); document.write( "10X^2-9000=1440X
\n" ); document.write( "10X^2-1440X-9000=0 FACTOUT THE 10
\n" ); document.write( "10(X^2-144X-900)=0
\n" ); document.write( "(X-150)(X+6)=0
\n" ); document.write( "X-150=0
\n" ); document.write( "X=150 MPH IS THE SPEED FO THE AIRPLANE IN STILL AIR.
\n" ); document.write( "PROOF
\n" ); document.write( "720/(150-30)+720/(150+30)=10
\n" ); document.write( "720/120+720/180=10
\n" ); document.write( "6+4=10
\n" ); document.write( "10=10\r
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