Question 1153051
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Let x be the half-life in years.  Then 1 year is (1/x) half-lives.<br>
{{{30(.5)^(1/x) = 27.5}}}
{{{.5^(1/x) = 11/12}}}
{{{(1/x)log(.5) = log(11/12)}}}
{{{x = log(.5)/log(11/12) = 7.97}}} to 2 decimal places<br>