Question

The following manufactured products have a nominal time of 80 minutes. Samples of five observations each have been taken, and the results are as listed. Using two SPC techniques, determine the upper and lower control limits (using a 99% level of significance) and respond to the following questions: Present your control charts and briefly discuss your findings.

Sample 1: 78 80 79 78 80 81

Sample 2: 77 78 79 79 75 81

Sample 3: 79 81 80 79 80 79

Sample 4: 77 80 80 79 80 81

Sample 5: 81 76 80 80 78 82

Please show work!

Answer 1

We can solve the given problme using Excel. Afyter feeding in the sample in excel we need to calculate the following using the following formula in Excel:

The above sheet will give following results

Now we can easily plot the results to get our control chart:

Here Upper/lower confidence limit is calculated using the formula:

Where, is sample mean

is z value for 99% confidence interval

is standard deviation and

n is sample size.

Form the given control chart we know that our process is within the control limits and thus process is under control.