document.write( "Question 571607: A substance has a half life of 23 hours .How old is the object that has 5% of the substance left? \r
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Algebra.Com's Answer #368157 by ankor@dixie-net.com(22740)\"\" \"About 
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A substance has a half life of 23 hours .
\n" ); document.write( "How old is the object that has 5% of the substance left?
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\n" ); document.write( "The radioactive decay formula:
\n" ); document.write( "A = Ao*2^(-t/h), where
\n" ); document.write( "A = resulting amt after t
\n" ); document.write( "Ao = initial amt (t-0)
\n" ); document.write( "t = time of decay
\n" ); document.write( "h = half-life of substance
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\n" ); document.write( "Let initial amt = 1, then we can write the equation
\n" ); document.write( "1*2^(-t/23) = .05
\n" ); document.write( "Using nat logs and the log equiv of exponents
\n" ); document.write( "\"-t%2F23\" = \"ln%28.05%29%2Fln%282%29\"
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\n" ); document.write( "\"-t%2F23\" = -4.3219
\n" ); document.write( "multiply both sides by -23
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\n" ); document.write( "You can check this on a good calc: enter: 2^(-99.4/23), results: .05 which is 5%
\n" ); document.write( "t = 99.4 days to a 5% remaining
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