9.2

21.

  1. This is a false statement because the interpretation implies that the population mean varies rather than the interval, which is very different.
  2. This is correct.
  3. This statement is false because the interpretation talks about the individuals and not the mean.
  4. This statement is false because the interpretation should be about the mean number of hours worked by adult Americans.

23. There is a 90% confidence that the mean drive-through service time is between 161.5 and 164.7 seconds.

25. By increasing the sample size and decreasing the confidence the confidence interval is narrowed.

31.

  1. x bar =58.71/12 = 4.893

  2. s=0.319 t(0.025)=2.201

    Lower bound: 4.893-2.201x0.319/root 12=4.690

    Upper bound: 4.893+2.201x0.319/root 12=5.096

    95% confident that the mean is between 4.960 and 5.096

  3. t(0.005)=3.106

    Lower bound: 4.893-3.106x0.310/root12=4.607

    Upper bound: 4.893+3.106x0.319/root 12=5.179

    99% confident that the mean is betwen 4.607 and 5.179

  4. The margin of error increases as the confidence level increases

32.

  1. x bar = 666.79/8 = 83.349

  2. s=12.324 t(0.025)=2.365

    Lower bound: 83.349-2.365x12.324/root 8=73.044

    Upper bound: 83.349+2.365x12.324/root8=93.65

    95% confident that the mean is betwen 73.044 and 93.65

  3. To increase the precision, decrease the level of confidence.

33.

  1. 0.961>0.918, therefore it is reasonable to conclude the data comes from a normal population.

  2. The confidence interval would be narrower because there is less variability.