A sample of 20 pages was taken without replacement from the 1,591-page phone directory(adsbygoogle = window.adsbygoogle || []).push({});

Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured(a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below:

0 260 356 403 536 0 268 369 428 536

268 396 469 536 162 338 403 536 536 130

Questions to answer are:

(a) Construct a 95 percent confidence interval for the true mean. (b) Why might normality be an

issue here? (c) What sample size would be needed to obtain an error of ±10 square millimeters

with 99 percent confidence? (d) If this is not a reasonable requirement, suggest one that is. (Data

are from a project by MBA student Daniel R. Dalach.) DisplayAds

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# Question on Confidence Interval and 95%

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