Certified Six Sigma Black Belt Exam Practice 5 — Questions and Answers
Question 1: A Black Belt uses the DMAIC roadmap for an existing process problem. When should a DFSS (DMADV) approach be used instead?
- When the process has too many defects to count
- When no existing process exists or the current process cannot meet requirements even with improvement (Correct answer)
- When the improvement timeline is too short for DMAIC
- When the project sponsor prefers a design approach
Correct answer: When no existing process exists or the current process cannot meet requirements even with improvement
DFSS/DMADV is applied when designing a new process or product, or when the existing process is fundamentally incapable of meeting customer requirements.
Question 2: In the Control phase, which tool is most appropriate for ensuring long-term process discipline after the Black Belt disengages?
- Fishbone diagram
- Control plan (Correct answer)
- Scatter diagram
- Affinity diagram
Correct answer: Control plan
A control plan documents what to monitor, how to measure it, control limits, and response actions to sustain improvements.
Question 3: Which measure of central tendency is most resistant to the effect of extreme outliers?
- Mean
- Variance
- Median (Correct answer)
- Mode
Correct answer: Median
The median is a positional measure unaffected by extreme values, making it more robust than the mean for skewed distributions.
Question 4: A Black Belt is choosing between an EWMA and an Xbar-R chart. EWMA is preferred when:
- Subgroup size is greater than 10
- Detecting large, sudden shifts quickly is critical
- Detecting small, gradual process shifts is the priority (Correct answer)
- The data follows a non-normal distribution
Correct answer: Detecting small, gradual process shifts is the priority
EWMA (Exponentially Weighted Moving Average) charts are more sensitive to small sustained shifts by weighting recent data more heavily.
Question 5: The cost of poor quality (COPQ) includes which of the following?
- Prevention costs and appraisal costs only
- Internal failure, external failure, appraisal, and prevention costs (Correct answer)
- Only visible costs such as scrap and rework
- Customer satisfaction scores and NPS
Correct answer: Internal failure, external failure, appraisal, and prevention costs
The full COPQ model includes prevention, appraisal, internal failure, and external failure costs (PAF model).
Question 6: A team finds that reducing batch size in a manufacturing process decreases lead time significantly. This improvement is best explained by:
- Reduced inspection frequency
- Little's Law: Lead time = WIP ÷ throughput rate (Correct answer)
- Decreased cycle time per unit
- Improved worker efficiency
Correct answer: Little's Law: Lead time = WIP ÷ throughput rate
Little's Law demonstrates that reducing work-in-process (WIP) by smaller batch sizes directly reduces lead time.
Question 7: A Black Belt selects a fractional factorial design (2⁵⁻²) instead of a full factorial. The primary trade-off is:
- Fewer factors can be studied
- Higher-order interactions are confounded with main effects or lower-order interactions (Correct answer)
- The experiment cannot estimate main effects
- Replication is no longer possible
Correct answer: Higher-order interactions are confounded with main effects or lower-order interactions
Fractional factorial designs alias (confound) higher-order interactions with main effects or other interactions, reducing resolution.
Certified Six Sigma Black Belt Exam Practice 5
A Black Belt uses the DMAIC roadmap for an existing process problem.
When should a DFSS (DMADV) approach be used instead?