CISA Practice Question: Information Systems Operations and Business Resilience
An organization has an availability requirement of 99.99% for its online transaction processing system. The system's MTBF is 720 hours. What is the maximum allowable MTTR to meet this requirement?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
4.32 minutes
Availability = MTBF/(MTBF+MTTR). 0.9999 = 720/(720+MTTR) => MTTR = 720/0.9999 - 720 = 0.072 hours ≈ 4.32 minutes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
43.2 minutes
Why it's wrong here
This is too high for 99.99%.
- ✗
72 minutes
Why it's wrong here
This would give around 90% availability.
- ✓
4.32 minutes
Why this is correct
Calculation yields 0.072 hours, which is 4.32 minutes.
- ✗
7.2 minutes
Why it's wrong here
This would correspond to 99.9% availability.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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