Scanning errors at Wal-Mart. Refer to the National Institute for Standards and Technology...

Scanning errors at Wal-Mart. Refer to the National Institute for Standards and Technology (NIST) study of the accuracy of checkout scanners at Wal-Mart stores in California, presented in Exercise. 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 7.4 is inappropriate for this study.

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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.

A random sample of size n = 144 yielded  = .76.

a. Is the sample size large enough to use the methods of this section to construct a confidence interval for p? Explain.

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b. Construct a 90% confidence interval for p.

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c. What assumption is necessary to ensure the validity of this confidence interval?