document.write( "Question 1154139: A one engine plane can fly 120 mph in still air. If it can fly 490 miles with a tailwind in the same time that it can fly 350 miles against a headwind, what is the speed of the wind? \n" ); document.write( "

Algebra.Com's Answer #776509 by ikleyn(52781) $\"\"$ $\"About$

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document.write( "Let \"v\" be the speed of the wind.\r\n" );
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document.write( "Then the effective speeds of the plane are   120+v  mph  tailwind  and  120-v  against the headwind.\r\n" );
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document.write( "Therefore, the \"time\" equation is\r\n" );
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document.write( "     = \r\n" );
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document.write( "First, cancel the common factor 70 in both sides; then cross multiply. You will get\r\n" );
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document.write( "    7*(120-v) = 5*(120+v)\r\n" );
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document.write( "    840 - 7v  = 600 + 5v\r\n" );
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document.write( "    840 - 600 = 5v + 7v\r\n" );
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document.write( "    240       = 12v\r\n" );
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document.write( "      v       = 240/12 = 20.\r\n" );
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document.write( "ANSWER.  Speed of wind is 20 miles per hour.\r\n" );
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