Question

Exponential Growth and Decay

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

Answer 1

x = xi e^-kt
.95 = e^-9 k
ln .95 = -9k
k = .005699

.5 = e^-.005699 t
ln .5 = - .005699 t
t = 121.6 years