A parallel-series system consists of N subsystems
connected in series such that the system works if
and only if all the subsystems work wherein
subsystem n (1 5 n I N) consists of m, components
connected in parallel such that the subsystem fails if
and only if all the components in this subsystem fail.
Figure 1 shows such a parallel-series configuration.
The reliability of such a parallel-series system is
expressed as: