81 Scanning errors at Wal-Mart. The National Institute for Standards and Technology (NIST) conducted a study of the accuracy of checkout scanners at Wal-Mart stores in California. NIST sets standards so that no more than 2 of every 100 items scanned through an electronic checkout scanner can have an inaccurate price. Recall that in a sample of 60 Wal-Mart stores, 52 violated the NIST scanner accuracy standard ( Tampa Tribune , Nov. 22, 2005). Suppose you want to estimate the true proportion of Wal-Mart stores in California that violate the NIST standard.

a. Explain why the large-sample methodology of Section 4 is inappropriate for this study.

b. Determine the number of Wal-Mart stores that must be sampled in order to estimate the true proportion to within .05 with 90% confidence, using the large-sample method.