A sample of 20 pages was taken from a Yellow Pages directory. 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:

(a) Construct a 95 percent confidence interval for the true mean.
(b) What sample size would be needed to obtain an error of ±20 square millimeters with 95 percent confidence? (Data DisplayAds are based on a project by MBA student Daniel R. Dalach.)

Transcribed Image Text:

0 260 56 403 536 0 268 369 428 536 268 396 469 536 162 338 40 536 536 130