9.2

21.

  1. Not reasonable, flawed because it states the probability.
  2. Reasonable.
  3. Not reasonable, flawed because it references individuals and not the mean.
  4. Not reasonable, flawed because the intepretation should be on adult Americans, not adult Americans in Idaho.

23. They are 90% confident that the mean drive-through service time is between 161.5 seconds and 164.7 seconds.

25. Decrease level of confidence and increase sample size.

31.

  1. 4.89.
  2. We are 95% confident that the mean pH of rainwater in Tucker County, West Virginia is between 4.69 and 5.096.
  3. We are 99% confident that the mean pH of rainwater in Tucker County, West Virginia is between 4.607 and 5.179.
  4. As confidence level increases, margin of error increases.

32.

  1. 72.1.
  2. We are 99% confident that the mean tax paid for a three-day business trip is between 61.799 and 82.401.
  3. increase sample size.

33.

  1. We are 95% confident that the mean repair cost for a low impact collision involving mini or micro vehicles is between 1035.8 and 2477.2 dollars.
  2. narrower.