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Scott Ward - week 1 day 7 e-text questions

Scott Ward - week 1 day 7 e-text questions - 8.48 A sample...

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8.48 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 (a) Construct a 95 percent confidence interval for the true mean. x-bar = 346.5 s= 170.38 95% Confidence Interval with differential freedom of 19 = 2.09 E = 2.09 x (170.38/ sqrt(20)) = 79.63 95% CI = (346.5 + 79.63, 346.5 – 79.63) (b) Why might normality be an issue here? Since this is a random sample, it most likely will not show the whole population, since confidence intervals are about whole population. (c) What sample size would be needed to obtain an error of ±10 square millimeters with 99 percent confidence? N = (t x s / E) N= (2.09 x 170.38/10)^2 = 1268.03, roughly 1270 (d) If this is not a reasonable requirement, suggest one that is. Decreasing the confidence level will lower the sample size needed.

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