I need to know how to:
(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.
A sample of 20 pages was taken without replacement from the 1,591-page phone directory 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
This solution shows how to construct a confidence interval for a mean, explains why normality is important when sample sizes are small, and finds an appropriate sample size.