  Let $n$ be a large number. A subset $A$ of $Z_n$ is complete if $S_A = Z_n$,
where $S_A$ is the collection of the subset sums of $A$. Olson proved that if
$n$ is a prime and $|A|> 2n^{1/2} $, then $S_A$ is complete. We show that a
similar result for the case when $n$ is a composite number, using a different
approach.
