The activity of a certain isotope dropped from 3200 ci to 800 ci in 24.0 years. what is the half-life of this isotope (in years) ? show your work.

Ln (800/3200) = - kt

t = 24 years.

ln (0.25) = - k*24

( - 1.3863) = - k*24

1.3863 / 24 = k

0.05776 = k

ln (0.5) = - k*t

-0.6931 = - 0.05776 t

12 = t

I don't know if you can just look at the question and know the answer. If 24 years is a quarter life then is it obvious that the 1/2 life is 12 years? It might be, but the method I've used works for sure.