  In this paper, we present methods of obtaining single moments of order
statistics arising from posibly dependent and non-identically distributed
discrete random variables. We derive exact and approximate formulas convenient
for numerical evaluation of such moments. To demonstrate their use, we tabulate
means and second moments of order statistics from random vectors having some
typical discrete distributions with selected parameter values. Next, we apply
our results in reliability theory. We establish moments of discrete lifetimes
of coherent systems consisting of heterogeneous and not necessarily
independently working components. In particular, we obtain expression for
expectations and variances of lifetimes of such systems. We give some
illustrative examples.
