document.write( "Question 423288: An airplane flew for 3 hours with a tail wind of 18 kilometers per hour. The return flight against the wind took 4 hours. Find the rate of the plane in still air. \n" ); document.write( "

Algebra.Com's Answer #853217 by greenestamps(13258) $\"\"$ $\"About$

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\n" ); document.write( "The distances are the same, and the ratio of the times in the two directions is 3:4; that means the ratio of the speeds in the two directions is 4:3.

\n" ); document.write( "If the plane's speed in still air is x, then the speed with the wind is x+18 and the speed against the wind is x-18:

\n" ); document.write( " $\"%28x%2B18%29%2F%28x-18%29=4%2F3\"$
\n" ); document.write( " $\"4%28x-18%29=3%28x%2B18%29\"$
\n" ); document.write( " $\"4x-72=3x%2B54\"$
\n" ); document.write( " $\"x=126\"$

\n" ); document.write( "ANSWER: 126 km/h

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