document.write( "Question 151179: a plane flies 900 miles with a tail wind, in 3 hours. It takes the same plane 4 hours to fly the 900 miles when flying against the wind. What is the planes speed in still air? \n" ); document.write( "
Algebra.Com's Answer #111150 by ankor@dixie-net.com(22740)\"\" \"About 
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a plane flies 900 miles with a tail wind, in 3 hours. It takes the same plane 4 hours to fly the 900 miles when flying against the wind. What is the planes speed in still air?
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\n" ); document.write( "Let x = speed of the plane
\n" ); document.write( "Let y = speed of the wind
\n" ); document.write( "then
\n" ); document.write( "(x+y) = ground speed with the wind
\n" ); document.write( "and
\n" ); document.write( "(x-y) = ground speed against the wind
\n" ); document.write( ":
\n" ); document.write( "Two distance equations:
\n" ); document.write( "3(x+y) = 900 (with the wind)
\n" ); document.write( "4(x-y) = 900 (against the wind)
\n" ); document.write( ":
\n" ); document.write( "Simplify; divide the 1st equation by 3, and 2nd equation by 4:
\n" ); document.write( "x + y = 300
\n" ); document.write( "x - y = 225
\n" ); document.write( "-------------addition eliminates y; find x
\n" ); document.write( "2x = 525
\n" ); document.write( "x = \"525%2F2\"
\n" ); document.write( "x = 262.5 mph
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\n" ); document.write( "Check solution:
\n" ); document.write( "Find the speed of the wind: 262.5 + y = 300; y = 37.5
\n" ); document.write( "3(262.5 + 37.5) = 900
\n" ); document.write( "4(262.5 - 37.5) = 900
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