9.2

21.

  1. flawed; this interpretation implies that the population mean varies rather than the interval.
  2. correct
  3. flawed; this interpretation makes an implication about individuals rather than the mean.
  4. flawed; this interpretation should be about the mean number of hours worked by adult americans, not 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. 1. increase the sample size 2. decrease the level of confidence to narrow the confidence interval

31.

  1. 4.893
  2. lower bound: 4.690, upper bound: 5.096. we are 95% confident that the mean ph of mean water in tucker county 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 county is between 4.607 and 5.179
  4. as the level of confidence increases, the margin of error also increases

32.

  1. Type answer here.
  2. Type answer here.
  3. Type answer here.

33.

  1. lower bound: 1035.8, upper bound: 2477.2; 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
  2. The 95% confidence interval would likely be narrower because there is less variability in the data because the variability associated with make of the vehicle has been removed.