Comments on "The Reliability of Periodically Repaired n - 1/n Parallel Redundant Systems

In the correspondence
¹
the author presented an approximate formula for the average failure rate in a periodically repaired n - 1/n parallel redundant system. It was assumed that the system consists of n parallel identical elements, each of which has a constant failure rate λ. The system is also repaired every T hours. It was shown that an approximate expression for the average failure rate of such a system is n(n - 1) λ
²
T/2. Upper and lower bounds were also given. In this comment a closed form exact expression for the average failure rate is presented.