312-50V13 Question #577: Real Exam Question with Answer & Explanation

Question

The change of a hard drive failure is once every three years. The cost to buy a new hard drive is $300. It will require 10 hours to restore the OS and software to the new hard disk. It will require a further 4 hours to restore the database from the last backup to the new hard disk. The recovery person earns $10/hour. Calculate the SLE, ARO, and ALE. Assume the EF = 1(100%). What is the closest approximate cost of this replacement and recovery operation per year?

Options

• A$1320
• B$440
• C$100
• D$146

Explanation

Explanation

Option D ($146) is correct because when you calculate the Single Loss Expectancy (SLE), you add the hard drive cost ($300) plus labor costs (10 + 4 = 14 hours × $10/hour = $140), giving an SLE of $440. The Annual Rate of Occurrence (ARO) is 1 failure every 3 years, or 0.33, and the Annual Loss Expectancy (ALE) = SLE × ARO = $440 × 0.33 ≈ $146.

• Option A ($1,320) is wrong because it incorrectly multiplies $440 × 3 (using 3 years instead of dividing by it), reversing the ARO calculation.
• Option B ($440) is the SLE - the total cost of a single incident - not the annualized cost; it ignores the ARO conversion.
• Option C ($100) is wrong as it only approximates the labor cost (14 hrs × $10) and ignores both the hardware cost and the annualization step.

💡 Memory Tip: Remember the formula chain - SLE × ARO = ALE. When a failure happens once every N years, the ARO = 1/N (not N itself). Think of ARO as "how often per year," so every 3 years means only 0.33 of an event happens annually.

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