How is availability for repairable items quantified?

Availability for repairable items is quantified as the ratio of Mean Time Between Failures (MTBF) to the sum of MTBF and Mean Time To Repair (MTTR). This calculation reflects how much time a system is operational between failures (MTBF) compared to the total time that includes the time it is operational and the time it is being repaired (MTBF + MTTR).

This formula emphasizes the importance of both the reliability of the system (as indicated by MTBF) and the efficiency of the repair process (MTTR). A higher MTBF means the system is reliable and operates for longer periods before encountering failures, which in turn increases availability. Conversely, if the MTTR is low, the system can return to operation quickly, further enhancing availability.

The other options mention various forms of MTBF and MTTR, but they incorrectly adjust the ratios or mix in other terms like Mean Time To Failure (MTTF), which is not suitable for measuring the availability of repairable items as it applies to non-repairable items. Thus, the proper formula for quantifying availability in this context is the ratio of MTBF to the total of MTBF and MTTR.