Posted by kela on Friday, November 9, 2012 at 6:00pm.
general equation
amount = starting (1/2)^(t/k) , where t is the time and k is the half-life period
a)
.945 = 1(.5)^1/k
ln .945 = (1/k)ln.5
1/k = ln.945/ln.5
k = ln.5/ln.945 = 12.25 years
b)
.65 = (.5)^t/12.25
t/12.25 = ln.65/ln.5 = .621488..
t = 7.61 years
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