ITPEC FE Morning April 2021 Question 16
Topic: System Component
Which of the following is the approximate availability of a system in percentage when the MTBF is 30 days and the MTTR is 6 hours?
Explanation
99.17% — availability is MTBF divided by MTBF plus MTTR, with both in the same unit.
- •MTBF: 30 days × 24 = 720 hours
- •Availability: 720 ÷ (720 + 6) = 720 ÷ 726 ≈ 0.9917, that is 99.17%
Answer (d)
Why not others:
- •(a) 0.83 — 6 ÷ 726 as a percentage: the unavailability, the share of time spent in repair
- •(b) 83.33 — 30 ÷ (30 + 6): adds 30 days to 6 hours as if they were the same unit
- •(c) 98.36 — equals 360 ÷ 366, what a 12-hour day gives; a day of operation here is 24 hours
Key rule: Convert MTBF and MTTR to the same unit before computing MTBF ÷ (MTBF + MTTR), and check whether the question asks for availability or its complement.
System Component · AI-written, may contain errors
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