Exam 11: Inferences About Population Variances

A random sample of 21 checking accounts at a bank showed an average daily balance of $430 with a standard deviation of $50. a.Provide a 95% confidence interval estimate of the variance of the population of the checking accounts. b.Provide a 95% confidence interval estimate of the standard deviation of the population of the checking accounts.

A sample of 16 students showed that the variance in the number of hours they spend studying is 25. At 95% confidence, test to see if the variance of the population is significantly different from 30. Use the critical value approach.

Exhibit 11-8 -Refer to Exhibit 11-8. The test statistic has a value of

Which of the following has a chi-square distribution?

The producer of a certain bottling equipment claims that the variance of all their filled bottles is 0.027 or less. A sample of 30 bottles showed a standard deviation of 0.2. The p-value for the test is

The sampling distribution used when making inferences about a single population's variance is

A sample of n observations is taken from a population. The appropriate chi-square distribution has

The average grade of a sample of 30 students on their second statistics examination was 85 with a standard deviation of 11. Is the variance of the population significantly more than 80? Use a 0.05 level of significance.

A machine produces pipes used in airplanes. The average length of the pipe is 16 inches. The acceptable variance for the length is .3 inches. A sample of 25 pipes was taken. The average length in the sample was 15.95 inches with a variance of .4 inches. a.Construct a 95% confidence interval for the population variance. b.State the null and alternative hypotheses to be tested. c.Compute the test statistic. d.The null hypothesis is to be tested at the 5% level of significance. State the decision rule for the test using the critical value approach. e.What do you conclude about the population variance?

A company claims that the standard deviation in their delivery time is less than 5 days. A sample of 27 past customers is taken. The average delivery time in the sample was 14 days with a standard deviation of 4.5 days. At 95% confidence, test the company's claim. Use the critical value approach.

The producer of a certain medicine claims that their bottling equipment is very accurate and that the standard deviation of all their filled bottles is 0.1 ounce or less. A sample of 20 bottles showed a standard deviation of 0.11. The test statistic to test the claim is

The grades of a sample of 5 students, selected from a large population, are given below. a.Determine a point estimate for the variance of the population. b.Determine a 95% confidence interval for the variance of the population. c.At 90% confidence, test to determine if the variance of the population is less than or equal to 50.

The manager of the service department of a local car dealership has noted that the service times of a sample of 30 new automobiles has a standard deviation of 6 minutes. A 95% confidence interval estimate for the standard deviation of the service times for all their new automobiles is

Exhibit 11-5 -Refer to Exhibit 11-5. The null hypothesis is to be tested at the 5% level of significance. The critical value(s) from the table is(are)

We are interested in testing whether the variance of a population is significantly less than 1.44. The null hypothesis for this test is

Exhibit 11-2 We are interested in determining whether or not the variances of the sales at two music stores (A and B) are equal. A sample of 26 days of sales at store A has a sample standard deviation of 30 while a sample of 16 days of sales from store B has a sample standard deviation of 20. -Refer to Exhibit 11-2. At 95% confidence the null hypothesis

Exhibit 11-6 We want to test the hypothesis that the population variances are equal. -Refer to Exhibit 11-6. The test statistic for this problem equals

A sample of 22 bottles of soft drink showed a variance of 0.64 in their contents. At 95% confidence, determine whether or not the standard deviation of the population is significantly different from 0.7. Use the critical value approach.

The chi-square value for a one-tailed (upper tail) hypothesis test at 95% confidence and a sample size of 25 is

The value of F_0.01 with 9 numerator and 20 denominator degrees of freedom is