IPA FE Subject A 2024 Question 4

Topic: System Component

A question IPA Japan published in 令和６年度 基本情報技術者試験 科目A 公開問題 問4, translated into English. ITPEC is based on the same exams.

The MTBF of a certain system in this fiscal year is 3,000 hours, and its MTTR is 1,000 hours. In the next fiscal year, when an improvement of 20% of this fiscal year’s value is made in the MTBF and an improvement of 10% of this fiscal year’s value is made in the MTTR, what is the availability in percent in the next fiscal year?

Explanation

80% — improving the MTBF lengthens it to 3,600 hours, improving the MTTR shortens it to 900 hours, and availability is MTBF ÷ (MTBF + MTTR).

  • •MTBF next year: 3,000 × (1 + 0.2) = 3,600 hours
  • •MTTR next year: 1,000 × (1 − 0.1) = 900 hours (a shorter repair time is the improvement)
  • •Availability: 3,600 ÷ (3,600 + 900) = 3,600 ÷ 4,500 = 0.8, that is 80%

This year’s availability is 3,000 ÷ 4,000 = 75%, so the improvements raise it by 5 points.

Answer (d)

Why not others:

  • •(a) 69 — both changes taken the wrong way: 2,400 ÷ (2,400 + 1,100) ≈ 0.686
  • •(b) 73 — the MTBF shortened by 20% instead of lengthened: 2,400 ÷ (2,400 + 900) ≈ 0.727
  • •(c) 77 — the MTTR lengthened by 10% instead of shortened: 3,600 ÷ (3,600 + 1,100) ≈ 0.766

Key rule: Availability = MTBF ÷ (MTBF + MTTR); improving the MTBF means making it longer, improving the MTTR means making it shorter.

System Component · AI-written, may contain errors

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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.