28) Statistical inference is the process by which ____

population characteristics are known with certainty.

sample data are summarized using graphs and pictures

population data are used to draw conclusions about a system of equations.

sample data are used to draw conclusions about a population.

29) A large corporation employs thousands of people worldwide. The average age of all employees is 46.8 years with a standard deviation of 6.4 years. A simple random sample (SRS) of 55 employees is selected, the sample mean is 45.2 years, and the sample standard deviation is 5.6 years. Which of the following is the value of a population parameter?

55

45.2

5.6

6.4

30) A sampling distribution is ____

a probability distribution that describes the possible values of a variable for all cases in the population.

always Normal.

a probability distribution that describes the possible values of the sample means from samples of a given size.

never Normally distributed.

31) A random variable, X, has mean = _X and standard deviation = _X. Suppose n independent, random observations of X are taken and the average,, of these n observations is computed. We can assert that if n is sufficiently large, the sampling distribution ofis approximately Normal. This assertion follows from the ____

law of large numbers.

central limit theorem.

definition of a sampling distribution.

68-95-99.7 rule.

32) Set up 1: The Office of Student Services at Western State University maintains information on the study habits of its full-time students. Their studies indicate that the mean amount of time undergraduate students study per week is 24 hours. The hours studied follows the normal distribution with a standard deviation of 5.5 hours. Suppose we select a random sample of 70 current students. What is the standard error of the mean?

0.657

5.5

0.252

2.001

33) Using Set up 1, what is the probability that the mean of this sample is between 23.5 hours and 24.5 hours?

0.9722

0.5531

0.0986

0.9104

34) Set up 2: The heights of fully grown white oak trees are normally distributed, with a mean of 90 feet and standard deviation of 4.2 feet. Random samples of size 7 are drawn from this population, and the mean of each sample is determined. The mean equals ____ and standard error of the mean of the sampling distribution is _____.

92 and 1.39

3.5 and 90

90 and 1.59

1.59 and 90

35)Using Set up 2, in any given sample, what is the likelihood that the mean is between 89 and 92.5 feet?

0.6250

0.6858

0.8604

0.6780

36) Set up 3: The tread life of tires mounted on light-duty trucks follows the normal probability distribution with a mean of 62,500 miles and a standard deviation of 4,800 miles. If the standard error of the mean is 845.15 what is the sample size to the nearest whole number?

35

30

4000

32

37) Using Set up 3, Suppose we select a sample of 50 tires and use a simulator to determine the tread life. What is the likelihood of finding that the sample mean is between 62,000 and 63,000?

0.4453

0.7705

0.5386

0.1147

38) Set up 4: A recent report found that 21% of U.S. households still have a landline telephone. Suppose a random sample of 200 homes was taken and a resident of the home was asked, "Do you have a landline telephone in your place of residence?" Of those asked, 46 said that they have a landline telephone. What is the probability that in the sample no more than 46 have a landline phone?

0.0749

0.4251

0.8405

0.7563

39) Using Set up 4, what is the probability that in the sample between 17% and 25% have a landline phone?

0.0749

0.4251

0.8351

0.7563

40) Using Set up 4, what is the probability that in the sample that more than 25% have a landline phone?

0.0824

0.4251

0.8351

0.7563

41) Using Set up 4, what is the 95% confidence interval for the proportion of homes with a landline phone?

(0.198, 0.302)

(0.188, 0.312)

(0.172, 0.288)

(0.209, 0.291)

42) Suppose a researcher knows the population standard deviation is 1.8 and constructs a 95% confidence interval (original interval) for the population mean from a sample of 60 with a sample mean of 10.4. If the researcher wishes to change the confidence level to 90% which of these statements is true about the new confidence interval?

The new confidence interval is smaller (narrower) than the original confidence interval because the standard error changes.

The new confidence interval is larger (wider) than the original confidence interval because the sample size must be reduced by 1 when using a new confidence level

The new confidence interval is the same size as the original interval.

The new confidence interval is smaller (narrower) than the original confidence interval because the margin of error changes.

43) Set up 5 A university surveyed recent graduates of the Accounting Department for their starting salaries. One hundred graduates returned the survey. The average salary was $43,700. The population standard deviation is $3,500. A 95% confidence interval is constructed. What does the confidence interval mean?

The population mean is in the interval.

The population mean is not in the interval.

The likelihood that any confidence interval based on a sample of 100 graduates will contain the population mean is 0.95.

There is a 5% chance the population mean is not within 95% of the interval.