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

The process is in statistical control

Answer

The point is within specification limits so no action is needed

Answer

The control limits need to be recalculated

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

Rule 1 — point beyond 3 sigma

Answer

Rule 3 — four of five in Zone B or beyond

Answer

Rule 4 — eight consecutive points on one 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

When the sample size is greater than 10

Answer

When data is collected in rational subgroups of 5

Answer

When the data follows a Poisson distribution

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 measures long-term variation while Cp measures short-term

Answer

Cpk uses control chart limits instead of specification limits

Answer

Cpk is only applicable to non-normal data

Question 5

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

Accepted Answer

Binomial distribution

Answer

Normal distribution

Answer

Poisson distribution

Answer

Exponential distribution

Question 6

A u-chart is preferred over a c-chart when which condition exists?

Accepted Answer

The sample size varies from subgroup to subgroup

Answer

The number of defects per unit follows a normal distribution

Answer

Only one type of defect is being tracked

Answer

The process is already in statistical control