anyhow, is an arithmetic sequence, review your book on it
so.. .let's see the terms
[tex]\bf \begin{array}{llll}
term&1&2&3
\\\\
value&\frac{1}{3}&\frac{5}{12}&\frac{1}{2}
\end{array}[/tex]
something was added to 1/3 to get 5/12
and something was added to 5/12 to get 1/2,
what the dickens was added anyway?
well, let's call it "d", or the "common difference"
you know, if something was added to the former term,
to get the latter, we can simply get their difference,
that is
subtract the former from the latter term, to get "d" :)
[tex]\bf \begin{cases}
\cfrac{5}{12}-\cfrac{1}{3}=\boxed{d}
\\\\
\cfrac{1}{2}-\cfrac{5}{12}=\boxed{d}
\end{cases}[/tex]
so, to get the value for the 4th term or day, simply add "d" that you found, to 1/2
