document.write( "Question 1121171: A department store sells 20 portable stereos per week at $80 each. The manager believes that for each decrease of $5 in the price, six more stereos will be sold. What price should be charged if the revenue needs to be $2240? \n" ); document.write( "

Algebra.Com's Answer #736956 by ikleyn(52781) $\"\"$ $\"About$

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document.write( "The condition says that at the price  (80 - 5x) dollars for one stereo the number of stereos sold will be  (20 + 6x),\r\n" );
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document.write( "where x is an integer number.\r\n" );
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document.write( "Then the problem ask to  find \"x\" in such a way that\r\n" );
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document.write( "    (80-5x)*(20+6x) = 2240.\r\n" );
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document.write( "    1600 - 100x + 480x - 30x^2 = 2240\r\n" );
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document.write( "    - 30x^2 + 380x - 640 = 0\r\n" );
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document.write( "    3x^2 - 38x + 64 = 0\r\n" );
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document.write( "     =  = .\r\n" );
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document.write( "Only positive integer root makes sense, which is  x= 2.\r\n" );
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document.write( "Answer.  The price under the question is  (80-5x) = 80 - 5*2 = 70 dollars.\r\n" );
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