Iron-59 has a half-life of 45.1 days. How old is an iron nail if the Fe-59 content is 25% that of a new iron sample? Please show the calculating so I can learn to do it.

Answer 1

k = 0.693/t_1/2
Solve for k and substitute into the below.
ln(No/N) = kt
No = 100
N = 25
k from above
Solve for t in days.