document.write( "Question 372366: strontium-89 has a half-life of 50.6 days. How long will it take for 20 grams of strontium-89 to decay to 8 grams? \n" ); document.write( "

Algebra.Com's Answer #265383 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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strontium-89 has a half-life of 50.6 days.
\n" ); document.write( " How long will it take for 20 grams of strontium-89 to decay to 8 grams?
\n" ); document.write( ":
\n" ); document.write( "The half life formula: A = Ao*2^(-t/h)
\n" ); document.write( "where
\n" ); document.write( "A = resulting amt after t time
\n" ); document.write( "Ao = initial amt
\n" ); document.write( "t = time
\n" ); document.write( "h = half-life of substance
\n" ); document.write( ":
\n" ); document.write( "20*2^(-t/50.6) = 8
\n" ); document.write( ":
\n" ); document.write( "2^(-t/50.6) = $\"8%2F20\"$
\n" ); document.write( ":
\n" ); document.write( "2^(-t/50.6) = .4
\n" ); document.write( ":
\n" ); document.write( "Using nat logs
\n" ); document.write( " $\"-t%2F50.6\"$ ln(2) = ln(.4)
\n" ); document.write( " $\"-t%2F50.6\"$ = $\"ln%28.4%29%2Fln%282%29\"$
\n" ); document.write( " $\"-t%2F50.6\"$ = -1.3219
\n" ); document.write( "t = -50.6 * -1.3219
\n" ); document.write( "t ~ 66.9 days
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