Co-60 is a beta emitter with a half-life of 5.3 years. Approximately what fraction of Co–60 atoms will remain in a particular sample after 26.5 years?
The equation for radioactive decay is given by
In this case, it is actually the ratio
So, the portion remaining is 0.03125 or 3.125 % which is
Note that I used the exponential form of the equation. You could also use the (simpler) form
if you rather.