Practice Problems - Supplement 6 (S6), Statistical Process Control

 Practice Problems: Supplement 6 (S6), Statistical Process Control 6S

Problem 1: Twenty-five engine mounts are sampled each day and found to have an average width of 3 inches, with a standard deviation of 0.2 inches. What are the control limits that include 95.45% of the sample means?

 Problem 2: Several samples of size n=8 have been taken from today’s production of fence posts. The average post was 4 yards in length and the average sample range was 0.021 yard. Find the 99.73% upper and lower control limits.

Problem 3: The average range of a process is 12 lbs. The sample size is 9. Use Table S6.1 to develop upper and lower control limits on the range.

Problem 4: Based on samples of 15 IRS auditors, each handling 200 files, we find that the total number of mistakes in handling files is 340. Find the 99.73% upper and lower control limits.

Problem 5: There have been complaints that the sports page of the Dubuque Register has lots of typos. The last 6 days have been examined carefully and the number of typos/page is recorded below. Is the process in control using Z = 3?

Day                          Number of Typos

Monday                          12

Tuesday                            5

Wednesday                     8

Thursday                          7

Friday                               6

Saturday                          0