Algebra.Com's Answer #821068 by ikleyn(52787)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "A cup of coffee contains 130 milligrams of caffeine.
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document.write( "If caffeine is eliminated from the body at a rate of 11% per hour,
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document.write( "how long will it take for 90% of this caffeine to be eliminated from a person's body
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document.write( "The decay equation is\r\n" );
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document.write( " M(t) =  =  .\r\n" );
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document.write( "To solve, divide both sides by 130\r\n" );
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document.write( " 0.1 =  \r\n" );
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document.write( "and take logarithm base 10 of both sides. We get then\r\n" );
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document.write( " log(0.1) = t*log(0.89)\r\n" );
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document.write( "and find \r\n" );
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document.write( " t =  = 19.76 hours. ANSWER\r\n" );
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document.write( "CHECK. The remaining mass is M(19.76) =  = 13.9984 milligrams, \r\n" );
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document.write( " which is a good precision, comparing with 13 milligrams.\r\n" );
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document.write( "Solved.\r
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