document.write( "Question 1102559: A pilot flew his single-engine airplane 90 miles with the wind from City A to above City B. He then turned around and flew back to City A against the wind. If the wind was a constant 20 miles per hour, and the total time going and returning was 1.3 hours, find the speed of the plane in still air. \n" ); document.write( "

Algebra.Com's Answer #717260 by ikleyn(52778) $\"\"$ $\"About$

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\n" ); document.write( "A pilot flew his single-engine airplane 90 miles with the wind from City A to above City B. He then turned around
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\n" ); document.write( "going and returning was 1.3 hours, find the speed of the plane in still air.
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document.write( "Let x be the speed of plane \"at no wind\", in miles per hour (mph).\r\n" );
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document.write( "Then the speed with the wind is (x+30) mph,\r\n" );
document.write( "     the speed against the wind is (x-30) mph.\r\n" );
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document.write( "Then the \"time equation\" is\r\n" );
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document.write( " +  = 1.3   hours.\r\n" );
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document.write( "90*(x+20) + 90*(x-20) = 1.3*(x^2-400)  ====>\r\n" );
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document.write( "180x = 1.3x^2 - 1.3*400  ====>  1.3x^2 - 180x - 1.3*400 = 0  ====>\r\n" );
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document.write( " =  = .\r\n" );
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document.write( "Only positive root makes sense  x =  = 141.29.\r\n" );
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document.write( "Answer.  The speed of the plane \"at no wind\" is 141.29 miles per hour.\r\n" );
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