I feel like this should have a rather simple solution using logarithms, but I don't quite know where to start.
Basically, every day I am going to multiply a given quantity by $r$, where $r < 1$.
Obviously, if $r$ is 0.5, then my half-life $n$ is 1 day. (This is also stated to remove any ambiguities on what counts as a day/range)
What is the relationship between $r$ and $n$?