A local men’s clothing store is being sold. The buyers are trying to estimate the percentage of items that are outdated. They will randomly sample among its 100,000 items in order to determine the proportion of merchandise that is outdated. Approximately how large a sample do the buyers need in order to insure that they are 90% confident that the margin of error is within 5%?

Solution: The 90% margin of error is given by

We want that the margin of error is within 5%

(because) Therefore, the sample size is.

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