Posted by TITA on Monday, November 23, 2009 at 7:19pm.
Fraction left at t = (1/2)^(t/T)
where T is the half life, which is 5 years in this case.
For the first question, solve
(1/2)^(2/5) = 75.8%
Repeat using the same formula for the other times t.
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