document.write( "Question 175912: A plain travels 560 miles to San Francisco and back. The trip there was with the wind. It took 7 hours. The trip back was into the wind. The trip back took 14 hours. Find the speed of the plain in still air and the speed of the wind. \n" ); document.write( "

Algebra.Com's Answer #131021 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"p\"$ = speed of plane in still air
\n" ); document.write( "Let $\"w\"$ = speed of the wind
\n" ); document.write( "with the wind:
\n" ); document.write( "(1) $\"d+=+%28p+%2B+w%29%2At%5B1%5D\"$
\n" ); document.write( "Against the wind:
\n" ); document.write( "(2) $\"d+=+%28p+-+w%29%2At%5B2%5D\"$
\n" ); document.write( "given:
\n" ); document.write( " $\"t%5B1%5D+=+7\"$ hrs
\n" ); document.write( " $\"t%5B2%5D+=+14\"$ hrs
\n" ); document.write( " $\"d+=+560\"$ mi
\n" ); document.write( "rewriting (1) and (2),
\n" ); document.write( "(1) $\"560+=+%28p+%2B+w%29%2A7\"$
\n" ); document.write( "(2) $\"560+=+%28p+-+w%29%2A14\"$
\n" ); document.write( "------------------------
\n" ); document.write( "(1) $\"7p+%2B+7w+=+560\"$
\n" ); document.write( "(2) $\"14p+-+14w+=+560\"$
\n" ); document.write( "Multiply (1) by $\"2\"$ and add to (2)
\n" ); document.write( "(1) $\"14p+%2B+14w+=+1120\"$
\n" ); document.write( "(2) $\"14p+-+14w+=+560\"$
\n" ); document.write( " $\"28p+=+1680\"$
\n" ); document.write( " $\"p+=+60\"$ mi/hr
\n" ); document.write( "(1) $\"560+=+%2860+%2B+w%29%2A7\"$
\n" ); document.write( " $\"560+=+420+%2B+7w\"$
\n" ); document.write( " $\"7w+=+140\"$
\n" ); document.write( " $\"w+=+20\"$ mi/hr
\n" ); document.write( "The plane's speed in still air was 60 mi/hr
\n" ); document.write( "the wind speed was 20 mi/hr \n" ); document.write( "

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