document.write( "Question 62429: need a system of equations for this prob: an airplane flew 4 hours against a wind of 40 km/h. on return he was flowing with the wind and flight was 3 hours. whats speed of airplane in still air. \n" ); document.write( "
Algebra.Com's Answer #43188 by funmath(2933)\"\" \"About 
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An airplane flew 4 hours against a wind of 40 km/h. On return he was flowing with the wind and flight was 3 hours. What's speed of airplane in still air.
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\n" ); document.write( "\"highlight%28d=rt%29\", d=distance, r=rate or speed, and t=time
\n" ); document.write( "Let the speed in still air be: x
\n" ); document.write( "Let the distance be:y
\n" ); document.write( "Then the trip against the wind can be modeled by the equation:
\n" ); document.write( "y=4(x-40)
\n" ); document.write( "The return trip can be modeled by (assuming that the wind didn't change speeds:
\n" ); document.write( "y=3(x+40)
\n" ); document.write( "Therefore, your system of equations is:
\n" ); document.write( "y=4(x-40)
\n" ); document.write( "y=3(x+40)
\n" ); document.write( ":
\n" ); document.write( "If you needed to find the speed of the airplane in still air, you'd let the two y's equal each other.
\n" ); document.write( "4(x-40)=3(x+40)
\n" ); document.write( "4x-160=3x+120
\n" ); document.write( "4x-3x-160=3x-3x+120
\n" ); document.write( "x-160=120
\n" ); document.write( "x-160+160=120+160
\n" ); document.write( "x=280
\n" ); document.write( "The speed in still air is: x=280 km/h
\n" ); document.write( "(You didn't ask, but for fun I thought you'd like to know that the trip was 960 km. Figure that out too if you want.)
\n" ); document.write( "Happy Calculating!!!
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