Question 1

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.

Accepted Answer

The answer of A random sample of 21 checking accounts...

Question 2

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.

Accepted Answer

The answer of A sample of 16 students showed that...

Question 3

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

Accepted Answer

A) 20.91 
B) 24.20 
C) 24.00 
D) 20.00

Question 4

Which of the following has a chi-square distribution?

Accepted Answer

A) (n - 1)$\sigma$2/S2 
B) (n - 2)$\sigma$2/S2 
C) (n - 1)S/$\sigma$ 
D) (n - 1)S2/$\sigma$2

Question 5

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

Accepted Answer

A) between 0.025 to 0.05 
B) between 0.05 to 0.01 
C) 0.05 
D) 0.025

Question 6

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

Accepted Answer

A) an F distribution 
B) a t distribution 
C) a chi-square distribution 
D) a normal distribution

Question 7

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

Accepted Answer

A) n degrees of freedom 
B) n - 1 degrees of freedom 
C) n - 2 degrees of freedom 
D) n - 3 degrees of freedom

Question 8

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.

Accepted Answer

The answer of The average grade of a sample of...

Question 9

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?

Accepted Answer

The answer of A machine produces pipes used in airplanes....

Question 10

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.

Accepted Answer

The answer of A company claims that the standard deviation...

Question 11

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

Accepted Answer

A) 400 
B) 22.99 
C) 4.85 
D) 20

Question 12

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.

Accepted Answer

The answer of The grades of a sample of 5...

Question 13

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

Accepted Answer

A) 16.047 to 45.722 
B) 4.778 to 8.066 
C) 2.93 to 6.31 
D) 22.833 to 65.059

Question 14

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)

Accepted Answer

A) 22.362 
B) 23.685 
C) 5.009 and 24.736 
D) 5.629 and 26.119

Question 15

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

Accepted Answer

A) Ho: $\sigma$2 o: s2 $\ge$ 1.44 
C) Ho: $\sigma$ o: $\sigma$2 $\ge$1.44

Question 16

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

Accepted Answer

A) should be rejected 
B) should not be rejected 
C) should be revised 
D) None of these alternatives is correct.

Question 17

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

Accepted Answer

A) 0.417 
B) .843 
C) 2.4 
D) 1.500

Question 18

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.

Accepted Answer

The answer of A sample of 22 bottles of soft...

Question 19

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

Accepted Answer

A) 33.196 
B) 36.415 
C) 39.364 
D) 37.652

Question 20

The value of F0.01 with 9 numerator and 20 denominator degrees of freedom is

Accepted Answer

A) 2.39 
B) 2.94 
C) 2.91 
D) 3.46

Exam 11: Inferences About Population Variances