Question

The half-life of stronium-90 is 28 years. How long will it take a 50-mg sample to decay to a mass of 32 mg? The formula below is an exponential decay formula:
`A(t)=A_(0) e^(-kt)`

Answer 1

Explanation:

So in ONE half life there will be 25 mg....use this info to calculate 'k'

25 = 50 e^(- k28)

ln (25/50) = -k 28

k = .024755

Now to find for 32 mg

32 = 50 e^-.024755 t <===== solve for t

ln (32/50) = -.024755 t

t = 18.0 years