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October 20, 2014

October 20, 2014

Posted by **Josh** on Saturday, October 22, 2011 at 7:23pm.

Find the half-life of a radioactive substance that decays by 5% in 9 years.

- Pre Calculus -
**Damon**, Saturday, October 22, 2011 at 7:29pmx = xi e^-kt

.95 = e^-9 k

ln .95 = -9k

k = .005699

.5 = e^-.005699 t

ln .5 = - .005699 t

t = 121.6 years

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