Exam 10: Inference About Means and Proportions With Two Populations

The results of a recent poll on the preference of voters regarding presidential candidates are shown below. At 95% confidence, test to determine whether or not there is a significant difference between the preferences for the two candidates.

To construct an interval estimate for the difference between the means of two populations when the standard deviations of the two populations are unknown, we must use a t distribution with (let n₁ be the size of sample 1 and n₂ the size of sample 2)

Exhibit 10-11 An insurance company selected samples of clients under 18 years of age and over 18 and recorded the number of accidents they had in the previous year. The results are shown below. We are interested in determining if the accident proportions differ between the two age groups. -Refer to Exhibit 10-11. The test statistic is

Samples of employees of Companies A and B provided the following information regarding the ages of employees. Develop a 97% confidence interval for the difference between the average ages of the employees of the two companies.

Exhibit 10-6 The management of a department store is interested in estimating the difference between the mean credit purchases of customers using the store's credit card versus those customers using a national major credit card. You are given the following information. -Refer to Exhibit 10-6. At 95% confidence, the margin of error is

Exhibit 10-9 Two major automobile manufacturers have produced compact cars with the same size engines. We are interested in determining whether or not there is a significant difference in the MPG (miles per gallon) of the two brands of automobiles. A random sample of eight cars from each manufacturer is selected, and eight drivers are selected to drive each automobile for a specified distance. The following data show the results of the test. -Refer to Exhibit 10-9. The mean for the differences is

During the primary elections of 2004, candidate A showed the following pre-election voter support in Tennessee and Mississippi. a.Develop a 95% confidence interval estimate for the difference between the proportion of voters favoring candidate A in the two states. b.Is there conclusive evidence that one of the two states had a larger proportion of voters' support? If yes, which state? Explain.