21 a. lower bound: 16.85 upper bound 19.95 b. Lower bound 17.12, upper bound: 19.68, increasing the sample size decreases themargin of error c lower bound: 16.32, upper bound: 20.48 increasing the level of conficence increases the margin or error d. if n=15 the pop must be normal

23 a. flawed; this interpretation implies that the population mean varies rather than the interval b. correct c. Flawed; makes an implication about individuals rather than the mean d.Flawed; the interpretation should be about the mean number of hours worked by adault Americans not about adaults in Idaho

25 we are 90% confident that the mean drive through service time of taco bel resaraunts is between 161.5 and 164.7 seconds

27 1 increases the sample size and 2 decreases the level of confidence to narrow the confidence interval

29 a since the distribution of blod alcohol concentration is not normally distributed, the sample must be large so that the distribution of the sample mean will be approximately normal. b. the sample size is less than 5% of the pop c. Lower bound: 0.1647, upper bound: 0.1693; we are 90% confident that the mean BAC in fatal crashes where hte driver had a positive BAC is beteeen 0.1647 and 0.1693g/dL d. yes. it is possible that the mean BAC is less than 8d/dL

31 lower bound:12.05 books, upper bound:14.75 books; we can be 99% confident that the mean number of books read by Americans in the past year is between 12.05 and 14.75

33 lower bound:1.08, upper bound:8.12 days, we can be 95% confident that the mean is between 1.08 and 8.12 days

5 x^2 0.95=10.117, X^2 0.005=30.114

7 x^2 0.99=9.542, x^2 0.01=40.289

9 a. lower bound: 7.94, upper bound:23.66 b. Lower bound:8.59, upper bound:20.63; the width of the interval decreases c. Lower bound:6.61, upper bound:31.36; the width of the interval increases

11 lower bound:1.612, upper bound: 4.278; we can be 95% Confident that the population standard deviation of the prices of 4GB memory cards is between 1.612 and 4.278

13 * lower bound:849.7, upper bound: 1655.3; we can be 90% confident that the population standard deviation of repair costs of a low impact bumper crash on a moni car is bwtween 849.7 and 1655.3 dollars*

summary(cars)
##      speed           dist       
##  Min.   : 4.0   Min.   :  2.00  
##  1st Qu.:12.0   1st Qu.: 26.00  
##  Median :15.0   Median : 36.00  
##  Mean   :15.4   Mean   : 42.98  
##  3rd Qu.:19.0   3rd Qu.: 56.00  
##  Max.   :25.0   Max.   :120.00

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