ITPEC FE Subject A April 2025 Question 12
ITPEC FE Subject A April 2025 — Question 12 of 60
Parallel vs Series Availability — calculate the difference between two system configurations.
Each device has availability A = 0.9.
Condition (1) — Parallel (at least one device running):
- Formula: 1 - (1 - A)²
- 1 - (1 - 0.9)² = 1 - 0.01 = 0.99
Condition (2) — Series (both devices must run):
- Formula: A × A
- 0.9 × 0.9 = 0.81
Difference: 0.99 - 0.81 = 0.18
Why not others:
- (a) 0.09 — this is just 1 - A, not a valid calculation here
- (b) 0.10 — incorrect parallel availability computation
- (d) 0.19 — arithmetic error
Key rule: "At least one" → parallel: 1 - (1-A)(1-B). "Both required" → series: A × B.
AI-generated — may contain errors
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