Note in 31 and 33 there are some tedious calculations that I did for you. You can see the output once you knit this file.

9.2

21.

  1. This is flawed because it suggests that the population mean varies instead of the individual.

  2. This is correct.

  3. This is flawed because it talks about individuals rather than the mean.

  4. This is flawed because it should be about the average number of hours worked by adult Americans, not about the adults in Idaho.

23.

It means that we are 90% confident that the average drive-through service time is between 161.5 and 164.7 seconds.

25.

You could increase the sample size and decrease the confidence level.

27.

  1. Because the distribution of BACs is not normal, the sample must be large so that the mean won’t be too skewed.

  2. The sample size is less than 5% of the population.

  3. Lower bound: 0.1647, Upper bound: 0.1693. We are 90% confident that the mean BAC in fatal crashes where the driver had a positive BAC is between these two bounds.

  4. Yes, it’s possible that the mean BAC is less than 0.08g/dL because it’s possible that the true mean is not captured in the confidence interval.

29.

Lower bound: 317.64 licks, Upper bound: 394.57 licks. We are 95% confident that the number of licks to the center of a Tootsie pop is between these bounds.

31.

  1. 4.8925

  2. 0.3194064

data <- c(4.58,5.72,5.19,4.75,5.05,5.02,4.8,4.74,4.77,4.76,4.77,4.56)
mean(data)
## [1] 4.8925
sd(data)
## [1] 0.3194064

  1. Lower bound: 4.606, Upper bound: 5.179, 99% confidence.

  2. 0.996 > 0.918, so the data came from a normal population.

33.

  1. skip

  2. skip

data2 <- c(3148,2057,1758,663,1071,2637,3345,773,743,1370)
mean(data2)
## [1] 1756.5
sd(data2)
## [1] 1007.454

  1. Lower bound: $1035.8, Upper bound: $2477.2, 95% confidence.

  2. The 95% 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.

9.3

5.

10.117, 30.144

7.

9.5542, 40.289

9.

  1. Lower bound: 7.94, Upper bound: 23.66

  2. Lower bound: 8.59, Upper bound: 20.63

  3. Lower bound: 6.61, Upper bound: 31.36

11.

Lower bound: 0.226, Upper bound: 0.542, 95% confident.

13.

Lower bound: $734.8, Upper bound: $1657.5, 90% confident.