Which formula is used to calculate availability?

The correct formula to calculate availability is derived from the relationship between Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR). Availability is a measure of a system's operational performance and is calculated to express the proportion of time a system is functioning correctly compared to the total time it is expected to be operational.

The formula for availability can be represented as MTBF divided by the total time of operational potential, which combines both the time the system is functioning (MTBF) and the time it is being repaired (MTTR). Thus, the correct expression would be:

Availability = MTBF / (MTBF + MTTR)

This denotes the fraction of the total time when the system is available for use. It's crucial because it highlights how downtime (repair time) affects overall availability.

The chosen answer can be related to the concept of calculating the availability percentage, which reflects the effective uptime of a system. Therefore, it's essential to ensure that the interpretation and calculation align with the overall framework of understanding system availability.

This option demonstrates a fundamental understanding of how availability is quantified and why it is significant in systems management and engineering contexts.