# algebra

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The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.4% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?

• algebra -

x = A e^-kt
if x/A = 0.5, t = 2.52*10^5

.5 = e^-k(2.52*10^5)

ln .5 = -.693 = -2.52*10^5 k
k = 2.75*10^-6

0.984 = e^-2.75*-10^-6 t
t = 5863 years

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