ITPEC IP April 2025 Question 16
ITPEC IP April 2025 — Question 16 of 100
0.86 — first calculate the parallel web tier, then combine it with the required database server.
A web server fails with probability 1 - 0.8 = 0.2. Both independent web servers fail with probability 0.2 × 0.2 = 0.04, so at least one works with probability 1 - 0.04 = 0.96. The database must also work, giving 0.96 × 0.9 = 0.864, which rounds to 0.86.
Answer (c)
Why not others:
- (a) 0.04 is only the probability that both web servers fail
- (b) 0.58 does not combine the parallel and serial stages correctly
- (d) 0.96 is only the web-tier availability and ignores the database
Key rule: Parallel availability is one minus the probability that every parallel component fails; multiply stages that are all required.
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