There are four general ways to improve reliability. One of the most popular of these solutions is to add surplus com-ponents to the subsystems of a system (known as RRAP) and the reliability-redundancy allocation problem. In a sub-system, how these surplus components are used is of particular importance. How to use surplus components in the subsystem is known as. There are three general strategies for reliability issues known as active, stored, and mixed strategy. The main aim of the study is to create a new formula on the basis of the subsystems that use these two strategies. Model 4 provides a continuous limit of the Markov chain with continuous time. This new formula enables us to perform complex strategy calculations in a very short time and accurately. Finally the exact function obtained for mixed strategy Protective system ultra-fast gas turbine has been tested. Given the results, the new equation decreased the solution time besides the accurate estimation of the system’s reliability.