9.2

21.

  1. flawed - the interval varies, not the population mean
  2. correct
  3. flawed - this is about the individuals, not the mean
  4. flawed - it’s about all Americans

23. The confidence that the mean of service is between 161.5 and 164.7 seconds is 90%

25. decrease the confidence level, increase the sample size

31.

  1. 4.893
  2. lower: 4.69, upper: 5.096, we’re 95% confident the mean will fall between 4.69 and 5.096
  3. lower: 4.607, upper: 5.179, we’re 99% confident the mean will fall between 4.607 and 5.179
  4. the margin of error increases as the confidence level increases

32.

  1. 83.35
  2. lower: 73.05, upper: 93.65, we’re 95% confident the mean will fall between 73.05 and 93.65
  3. decrease the confidence level

33.

  1. lower: 1035.8, upper: 2477.2, we’re 95% confident the mean will fall between 1035.8 and 2477.2
  2. the interval would be narrower since there is less variability