If unavailability for a system with one failure mode is given as 0.002, what is the availability?

• A. 0.0002
• B. 0.02
• C. 0.98
• D. 0.998

Answer: (D)

To determine the availability of a system, you can use the relationship between availability, unavailability, and reliability. Availability is defined as the proportion of time a system is in a functioning condition, and it can be calculated using the formula:

Availability = 1 - Unavailability

In this case, the given unavailability for the system is 0.002. To find the availability, you can simply subtract the unavailability from 1:

Availability = 1 - 0.002

Availability = 1 - 0.002 = 0.998

This shows that the system is available 99.8% of the time. Thus, the correct answer is 0.998, which reflects a high level of system reliability and operational readiness, demonstrating that the system is largely dependable and only unavailable for a very small fraction of time.