CompTIA Server+ SK0-005 Practice Question

For a constant failure rate, the failure rate λ of one component is the reciprocal of its MTBF:

λ = 1 / 300 000 h ≈ 3.33 × 10⁻⁶ failures/h.

Three years of continuous service equal 3 × 365 × 24 = 26 280 h. The expected failures for one fan in that period are

26 280 h × 3.33 × 10⁻⁶ ≈ 0.088 failure.

With 50 identical fans, the expectation scales linearly:

50 × 0.088 ≈ 4.4 failures.

Rounded to the nearest whole unit, documenting about four fan-module failures over three years is the most accurate forecast. The smaller figure underestimates demand, while the larger figures assume a failure probability several times higher than that implied by the MTBF.