9.2

21.

  1. flawed because this intpretation implies that hte population mean varies instead of the interval
  2. correct
  3. flawed becaues this intpreatation makes an implication about the individual rather than the mean
  4. flawed because this intpretation should be about the mean worked by adult Americans, not just a small subgroup.

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

25. 1. Increase the sample size 2. Decrease the level of confidence to make the confidence interval smaller

31.

  1. 4.893
  2. (4.690, 5.096) ; we are 95% confident that the mean oh of water is between 4.690 and 5.096
  3. (4.607, 5.179) ; we are 99% confident that the mean ph of rain water is between 4.607 an 5.179
  4. As the level of confidence increases, the margin of error also increases.

32.

  1. 83.35
  2. (73.05, 93.65); we are 95% confident that the population mean will be between 73.05 and 93.65
  3. The researcher can reduce variabilty or lower the confidence level

33.

  1. (1035.8, 2477.2); we are 95% confident that the mean repair would be bewteen 1035.8 and 2477.2
  2. It would be narrower because there is less variability in the date