Molded fiberglass parts are to be tested for defectives. Two different grades of fiberglass were used for the parts, and one is interested in testing for a difference in the proportions defective using a: = 0.05.
(a) How many parts of each grade must be sampled in order to detect a difference in proportions defective of 0.1 with probability 0.8?
(b) The examination of 550 parts from the first grade of fiberglass resulted in 14 defectives. From 400 parts of the second grade of fiberglass there were 11 defectives. Conduct the test for differences, and explain what your results mean.