Cloud Digital Leader Scaling with Google Cloud operations Practice Question
A company's web service has a Service Level Objective (SLO) of 99.9% monthly availability. In a 30-day month, how many minutes of downtime are allowed before the SLO is violated?
⚠ Common exam trap
Test-takers frequently confuse 99.9% with 99.99% (four nines) and incorrectly calculate ~4.3 minutes, or they mistakenly compute 0.1% of 30 days in hours (0.072 hours) and then misread it as 7.2 hours.
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
✓
~43.2 minutes
The SLO of 99.9% monthly availability means the service can be unavailable for 0.1% of the total monthly time. In a 30-day month, total minutes are 30 × 24 × 60 = 43,200 minutes. 0.1% of 43,200 minutes is 43.2 minutes, so option B is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
~4.3 minutes
Why it's wrong here
4.3 minutes is the monthly downtime budget for 99.99% availability (four nines), not for 99.9% (three nines). A 99.9% SLO allows roughly 10x more downtime than 99.99%, so the correct three-nines budget is 43.2 minutes per 30-day month. Budgeting only 4.3 minutes would over-engineer your architecture beyond the stated requirement.
- ✓
~43.2 minutes
Why this is correct
In a 30-day month there are 43,200 minutes (30 × 24 × 60). 99.9% availability permits 0.1% downtime, so the error budget is 0.001 × 43,200 = 43.2 minutes. This is the classic 'three nines' SLO calculation and implies that a service can be unavailable for a total of 43 minutes and 12 seconds per month while still meeting the target.
- ✗
~7.2 hours
Why it's wrong here
7.2 hours equals 432 minutes, which is exactly 1% of a 30-day month. This corresponds to 99% availability (two nines), not 99.9%. Since 99.9% downtime is 0.1%, it is an order of magnitude more restrictive — the allowed downtime drops by a factor of 10, from 432 minutes down to 43.2 minutes.
- ✗
~8.6 hours
Why it's wrong here
8.6 hours per month corresponds to roughly 99% availability (two nines) for a 30-day month, but it is actually slightly more than the 7.2 hours (432 minutes) that exactly equals 1% downtime. A 99.9% availability target allows only 0.1% downtime — about 43.2 minutes — so 8.6 hours is roughly 12 times larger than the permitted error budget, reflecting a much lower availability goal.
Go deeper
Related to this question
Learn chapter
High Availability: 99.9% vs 99.99% vs 99.999%
Key term
SLO
A Service Level Objective is a measurable target for a specific aspect of a service's performance or reliability that a team commits to meeting over a defined period.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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