9.2

21.

  1. Flawed - interpretation implies population mean is varying
  2. correct
  3. Flawed - interpretation talks about entire population rather than just the sample population mean
  4. Flawed - interpretation discusses Idaho rather than all American adults discusssed in propmt

23. 90% confident that the mean service time at all Taco Bell’s is 161.5 and 164.7

25. use a lower confidence interval and a larger sample size.

31.

  1. 4.893
  2. 95% confident that the mean pH of rain water in Tucker County is between 4.690 and 5.096
  3. 90% confident that the mean pH of rain water in Tucker County is between 4.607 and 5.179
  4. M.O.E. increases with an increasing C.I.

32.

  1. 83.349
  2. we are 95% confident that the travel tax for a three day business trip is between 73.048 and 93.650
  3. Lower the confidence interval

33.

  1. 95% confident the mean repair cost for low-impact collisions involving both sized vehicles is between $1035.80 and $2477.20.
  2. narrower because there would be less variability in the data due to the same model of the cars.