9.2

21.

  1. this implies that the population mean varies rather than the interval.
  2. This is correct.
  3. this interpretation makes implications about individuals rather than the mean.
  4. This is not specific to adults in Idaho.

23. This means that we are 90% confident that the mean service time at the Taco Bell drive through is between 161.5 and 164.7 seconds.

25. Increasing sample size and decreasing the level of confidence

31.

  1. 4.893
  2. lower bound: 4.687 upper bound: 5.096– we are 95% confident that the mean ph of rain water in Tucker County is between these two values
  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 these two values.
  4. As the levels of confidene increases, the margin of error also inreases.

32.

  1. 83.348
  2. lower bound: 4.623 upper bound: 5.1567
  3. I would lower the confidence level.

33.

  1. lower bound: 1035.8, upper bound: 2477.2– we are 95% confident that the mean repair cost would be between these two values
  2. the 95% confidence interval would likely be narrower because there is less variability in the data because vrialibity associated with make of the vehicle is gone.