The activity of a sample of Ba-137m has decreased by 75% from its initial activity after 5.10 minutes. What is the half-life of Ba-137m? What fraction of activity remains after 6.25 minutes?

Question

(A=Aoe (-kt); k = .693/t1/2)

Answer 1

ln(No/N) = kt
No = 100
N = 100-75 = 25
k = ?
t = 5.10 minutes.
Solve for k, then
k = 0.693/(t_1/2>