We wish to study the quality of our production line. We take a random sample of 1000 widgets from our line. A quality rating was determined for each of the 1000 widgets, and the average quality rating in the sample was 4. The sample standard deviation was 0.5. Also, 6 of the 1000 widgets were found to be defective.

Estimate the average quality rating for widgets from our production line, and include the uncertainty in this estimate in the form, a ± b.