ITPEC IP October 2020 Question 15

Topic: System Component

When a computer system operates for 1,200 hours, the status of the normal operation time and the repair time is shown in the table below. What is the value of MTTR of the system?

Elapsed time (Hours)Status0through250Normal operation250through265Repair time265through580Normal operation580through600Repair time600through990Normal operation990through1,000Repair time1,000through1,200Normal operation

Explanation

15 — MTTR, the mean time to repair, is the total repair time divided by the number of repairs.

The repair rows of the table:

  • •250 through 265: 15 hours
  • •580 through 600: 20 hours
  • •990 through 1,000: 10 hours

Total repair time: 15 + 20 + 10 = 45 hours over 3 repairs, so MTTR = 45 ÷ 3 = 15 hours.

Answer (b)

Why not others:

  • •(a) 10 — the shortest single repair, 990 through 1,000, not the mean
  • •(c) 20 — the longest single repair, 580 through 600, not the mean
  • •(d) 45 — the total repair time, not yet divided by the 3 repairs

Key rule: MTTR is total repair time ÷ number of failures and MTBF is total operating time ÷ number of failures; together they give the availability, MTBF ÷ (MTBF + MTTR).

System Component · AI-written, may contain errors

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