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Confidence Interval for Purchasing a Large Collection

2. We are interested in purchasing a large collection of Palm M515 PDAs but need to have a general idea of how much we must pay for budgetary purposes. Thus, we will construct a confidence interval on the purchase price and in doing so we will assume that selling prices are close to being normally distributed. A sample of selling prices (rounded to the nearest dollar) of the Palm M515 PDA for a one-week selling period in November are listed below.

250 239 245 199 240 228 255 232
225 210 225 246 240 245 225 238
a. How do you know that you will need to construct the confidence interval using a t-distribution approach as opposed to a z-distribution?


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