A sample of 20 pages was taken from a Yellow Pages (yp.com) business 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:

0 260 356 403 536 0 268 369 428 536 268 396 469 536 162 338 403 536 536 130

(a) Construct a 95% confidence interval for the true mean. (Round your answers to 2 decimal places.)

The 95% confidence interval is from to .

(b) What sample size would be needed to obtain an error of 20 square millimeters with 95% confidence? (Enter your answer as a whole number (no decimals). Use a z-value taken to 3 decimal places in your calculations.)

Sample size