Lean Six Sigma Black Belt Certification Lean Six Sigma Black Belt Control Phase: SPC Questions and Answers 2

Question 1

A process has an X-bar chart with UCL = 50.5, CL = 50.0, and LCL = 49.5. If a single point plots at 50.7, what is the correct interpretation?

Accepted Answer

The process has a special cause variation

Answer

Any point plotting beyond a control limit signals a special cause of variation requiring investigation.

Question 2

Which Western Electric rule is violated when two out of three consecutive points fall in Zone A on the same side of the center line?

Accepted Answer

Rule 2 — two of three in Zone A

Answer

Western Electric Rule 2 triggers when two out of three consecutive points fall in Zone A (between 2σ and 3σ) on the same side.

Question 3

When should a Black Belt choose an Individuals and Moving Range (I-MR) chart over an X-bar and R chart?

Accepted Answer

When only one measurement per time period is available

Answer

I-MR charts are used when subgrouping is not possible and only individual measurements are available per sampling period.

Question 4

What is the primary purpose of calculating process capability index Cpk rather than Cp?

Accepted Answer

Cpk accounts for process centering relative to specification limits

Answer

Cpk accounts for both process spread and how well the process is centered between the specification limits.

Question 5

On a p-chart monitoring the fraction defective, what distribution is used to calculate the control limits?

Accepted Answer

Binomial distribution

Answer

The p-chart is based on the binomial distribution since it tracks the proportion of nonconforming units in a sample.

Lean Six Sigma Black Belt Certification Practice Test