Algebra.Com's Answer #835238 by ikleyn(52786)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "on a trip jennifer noticed that her car averaged 21 mi/gal of gas except
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document.write( "for the days she used the air conditioning, and then it averaged only 17 mi/gal.
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document.write( "if she use 91 gal of gas to drive 1751 mi, on how many of those miles
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document.write( "did she used the air conditioning?
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document.write( "Let x be the miles where she used the air conditioning.\r\n" );
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document.write( "Then miles where she didn't use the air conditioning were (1751-x).\r\n" );
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document.write( "Now we can write this equation for the total gas spent\r\n" );
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document.write( "  +  = 91 gallons of gas (total). (*)\r\n" );
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document.write( " | At this point, the setup is just complete, |\r\n" );
document.write( " | and our task is to solve this equation. |\r\n" );
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document.write( "For it, multiply both sides by 21*17. You will get\r\n" );
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document.write( " 17x + 21*(1751-x) = 91*21*17\r\n" );
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document.write( " 17x + 21*1751 - 21x = 32487\r\n" );
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document.write( " 17x - 21x = 32487 - 21*1751\r\n" );
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document.write( " -4x = -4284\r\n" );
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document.write( " x =  = 1071.\r\n" );
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document.write( "ANSWER. She used the air conditioning on 1071 miles.\r\n" );
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document.write( "CHECK. I will check if equation (*) is held.\r\n" );
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document.write( "  +  = 51 + 40 = 91 gallon of gas, in total. ! Correct !\r\n" );
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document.write( "Solved.\r
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