9.2

21.

  1. Shouldn’t be a probability statement.
  2. Correct.
  3. Shouldn’t be a proportion statement
  4. Flawed, the interpretion should be about the mean number of hours worked by adult Americans, not about adults in Idaho

23. We are 90% confident that the mean drive through service time of Taco Bell restaurants is between 161.5 and 164.7 seconds

25. Increase the sample size or decrease the level of confidence

31.

  1. 4.893
  2. Lower bound = 4.690 Upper bound = 5.096. We are 95% confident that the mean pH of rain water in Tucker Country is between 4.690 and 5.096.
  3. Lower bound = 4.607 Upper bound = 5.179. We are 99% confident that the mean pH of rain water in Tucker Country is between 4.607 and 5.179.
  4. As the level of confidence increases, the margin of error/width also increases.

32.

  1. 83.49
  2. Lower bound = 73.044 Upper bound = 93.653 We are 95% confident that the mean tax paid for a 3-day business trip is between 73.044 and 93.635.
  3. Decreasing the confidence level

33.

  1. Lower bound = 1035.80 Upper bound = 2477.2
  2. Narrower.