The strontium-87 isotopes stores in the body and decays by the process shown below. The half-life is 2.80hr. Suppose that 0.766 millicuries got into the body. How many mc will remain after 8.40 hr?

Answer 1

k = 0.693/t_1/2
Then
ln(No/N) = kt
No = 0.766
N = solve for this
k from above
t = 8.40 hr

Answer 2

2.30