21 a. Lower bound 16.85, Upper bound 19.95 b. Lower bound 17.12, Upper bound 19.68 c. Lower bound 16.32, Upper bound 20.48 Increasing the confidence level increases the margin of error. d. The population must be normal.
23 a. This implies that the population mean varies as opposed to the interval, so it is flawed. b. Correct c. This implies information about individuals rather than about the mean, so it is flawed. d. This should be about the mean of hours worked by American adults, not about adults in Idaho, so it is flawed.
25 90% confident
27 Increase the sample size and decrease the level of confidence
29 a. Large sample b. n<5% of the population c. Lower bound 0.1647, upper bound 0.1693 (90% confident) d. It’s possible but not likely
31 (12.05, 14.75) with 90% confidence
33 (1.08, 8.12) with 95% confidence