Example 6 mentioned closing prices for listings of the iPhone 5s on eBay. If you don€™t feel comfortable bidding (or can€™t wait until a listing has ended), you can often purchase the item right away at the indicated Buy It Now price. A random sample of Buy It Now prices for an unlocked iPhone 5s, 16GB and in new condition in July 2014 showed the following prices (in $) with dot plot and box plot shown in the figure: 618, 650, 608, 634, 675, 618, 625, 619, 630.

a. What must we assume to use these data to find a 95% confidence interval for the mean Buy It Now price on eBay? Do these assumptions seem plausible?
b. The table shows the way software reports results. How was the standard error of the mean (SE Mean) obtained?

c. Interpret the 95% confidence interval in context.
d. Compared to the confidence interval (569, 599) for prices from auctions obtained in Example 6, is there evidence that the mean price is higher when purchased through Buy It Now? Explain.
e. Excluding the observation of $675, the confidence interval equals (615, 636). Does this change your answer to part d?

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600 610 620 630 640 650 660 670 680 Buy It Now Price Variable N BuyItNow 9 630.78 20.47 Mean StDev SE Mean 95% CI 6.82 (615.04 646.52)