9.2

21.

  1. The statement is flawed because the interpretation implies that the poulation mean varies rather than the interval
  2. Correct
  3. It is false because the interpretation makes an implication about the individuals rather than the mean
  4. It is false because the interpretation should be about the mean number of hours worked by adult americans not about adults in Idaho

23. We are 90% confident that the mean drive through service time of Taco Bell resturants is between 161.5 and 161.7.

25. Increase the sample size and decrease the confindence level to narrow the confidence interval.

31.

  1. 4.893
  2. s = 0.319 t= 2.201 Lower bound: 4.690 Upper bound: 5.096 We are 95% confidence that the mean pH of rain water in Tucker County, West Virgina is between 4.690 and 5.096
  3. t = 3.106 Lower bound: 4.607 Upper bound: 5.179 We are 99% confident that the mean pH of rain water in Tucker County, West Virginia is between 4.607 and 5.179
  4. The margin of error increases as the confidence level decreases

32.

  1. x = 83.349
  2. s = 12.324 t= 2.365 Lower bound: 73.044 Upper bound: 93.654 We are 95% confident that the mean travel taxes for a three-day business trip is between $72.0044 and %93.654
  3. In order to increase the precision of interval, s/he should decrease level of confidence.

33.

  1. x = 1756.5 s = 1007.5 t = 2.262 Lower bound: 1035.8 Upper bound: 2477.2 We are 95% confident the mean repair cost for a low-impact collision involving mini- and micro-vehicles is between $1035.8 and $2477.2
  2. The confidence interval would likely be narrower because there is less variability in the data because variability associated with the make of the vehicle has been removed

hint:For #31 s = .319, #32 s = 12.32, #33 s = 1007.45