# Chapter 11 Practice

### 11.1 Facts About the Chi-Square Distribution

1.

If the number of degrees of freedom for a chi-square distribution is 25, what is the population mean and standard deviation?

2.

If $$df > 90$$, the distribution is _____________. If $$df = 15$$, the distribution is ________________.

3.

When does the chi-square curve approximate a normal distribution?

4.

Where is $$\mu$$ located on a chi-square curve?

5.

Is it more likely the df is 90, 20, or two in the graph?

### 11.2 Test of a Single Variance

Use the following information to answer the next three exercises: An archer’s standard deviation for his hits is six (data is measured in distance from the center of the target). An observer claims the standard deviation is less.

6.

What type of test should be used?

7.

State the null and alternative hypotheses.

8.

Is this a right-tailed, left-tailed, or two-tailed test?

Use the following information to answer the next three exercises: The standard deviation of heights for students in a school is 0.81. A random sample of 50 students is taken, and the standard deviation of heights of the sample is 0.96. A researcher in charge of the study believes the standard deviation of heights for the school is greater than 0.81.

9.

What type of test should be used?

10.

State the null and alternative hypotheses.

11.

$$df$$ = ________

Use the following information to answer the next four exercises: The average waiting time in a doctor’s office varies. The standard deviation of waiting times in a doctor’s office is 3.4 minutes. A random sample of 30 patients in the doctor’s office has a standard deviation of waiting times of 4.1 minutes. One doctor believes the variance of waiting times is greater than originally thought.

12.

What type of test should be used?

13.

What is the test statistic?

14.

What can you conclude at the 5% significance level?

### 11.3 Goodness-of-Fit Test

Determine the appropriate test to be used in the next three exercises.

15.

An archeologist is calculating the distribution of the frequency of the number of artifacts she finds in a dig site. Based on previous digs, the archeologist creates an expected distribution broken down by grid sections in the dig site. Once the site has been fully excavated, she compares the actual number of artifacts found in each grid section to see if her expectation was accurate.

16.

An economist is deriving a model to predict outcomes on the stock market. He creates a list of expected points on the stock market index for the next two weeks. At the close of each day’s trading, he records the actual points on the index. He wants to see how well his model matched what actually happened.

17.

A personal trainer is putting together a weight-lifting program for her clients. For a 90-day program, she expects each client to lift a specific maximum weight each week. As she goes along, she records the actual maximum weights her clients lifted. She wants to know how well her expectations met with what was observed.

Use the following information to answer the next five exercises: A teacher predicts that the distribution of grades on the final exam will be and they are recorded in Table 11.21.

A0.25
B0.30
C0.35
D0.10

Table 11.21

The actual distribution for a class of 20 is in Table 11.22.

A7
B7
C5
D1

Table 11.22

18.

$$df$$ = ______

19.

State the null and alternative hypotheses.

20.

$$\chi^2$$ test statistic = ______

21.

At the 5% significance level, what can you conclude?

Use the following information to answer the next nine exercises: The following data are real. The cumulative number of AIDS cases reported for Santa Clara County is broken down by ethnicity as in Table 11.23.

EthnicityNumber of cases
White2,229
Hispanic1,157
Black/African-American457
Asian, Pacific Islander232
Total = 4,075

Table 11.23

The percentage of each ethnic group in Santa Clara County is as in Table 11.24.

EthnicityPercentage of total county populationNumber expected (round to two decimal places)
White42.9%1748.18
Hispanic26.7%
Black/African-American2.6%
Asian, Pacific Islander27.8%
Total = 100%

Table 11.24

22.

If the ethnicities of AIDS victims followed the ethnicities of the total county population, fill in the expected number of cases per ethnic group.
Perform a goodness-of-fit test to determine whether the occurrence of AIDS cases follows the ethnicities of the general population of Santa Clara County.

23.

$$H_0$$: _______

24.

$$H_a$$: _______

25.

Is this a right-tailed, left-tailed, or two-tailed test?

26.

degrees of freedom = _______

27.

$$\chi^2$$ test statistic = _______

28.

Graph the situation. Label and scale the horizontal axis. Mark the mean and test statistic. Shade in the region corresponding to the confidence level.

Let $$\alpha = 0.05$$

Decision: ________________

Reason for the Decision: ________________

Conclusion (write out in complete sentences): ________________

29.

Does it appear that the pattern of AIDS cases in Santa Clara County corresponds to the distribution of ethnic groups in this county? Why or why not?

### 11.4 Test of Independence

Determine the appropriate test to be used in the next three exercises.

30.

A pharmaceutical company is interested in the relationship between age and presentation of symptoms for a common viral infection. A random sample is taken of 500 people with the infection across different age groups.

31.

The owner of a baseball team is interested in the relationship between player salaries and team winning percentage. He takes a random sample of 100 players from different organizations.

32.

A marathon runner is interested in the relationship between the brand of shoes runners wear and their run times. She takes a random sample of 50 runners and records their run times as well as the brand of shoes they were wearing.

Use the following information to answer the next seven exercises: Transit Railroads is interested in the relationship between travel distance and the ticket class purchased. A random sample of 200 passengers is taken. Table 11.25 shows the results. The railroad wants to know if a passenger’s choice in ticket class is independent of the distance they must travel.

Traveling distanceThird classSecond classFirst classTotal
1–100 miles2114641
101–200 miles1816842
201–300 miles16171548
301–400 miles12142147
401–500 miles661022
Total736760200

Table 11.25

33.

State the hypotheses.
$$H_0$$: _______
$$H_a$$: _______

34.

$$df$$ = _______

35.

How many passengers are expected to travel between 201 and 300 miles and purchase second-class tickets?

36.

How many passengers are expected to travel between 401 and 500 miles and purchase first-class tickets?

37.

What is the test statistic?

38.

What can you conclude at the 5% level of significance?

Use the following information to answer the next eight exercises: An article in the New England Journal of Medicine, discussed a study on smokers in California and Hawaii. In one part of the report, the self-reported ethnicity and smoking levels per day were given. Of the people smoking at most ten cigarettes per day, there were 9,886 African Americans, 2,745 Native Hawaiians, 12,831 Latinos, 8,378 Japanese Americans and 7,650 whites. Of the people smoking 11 to 20 cigarettes per day, there were 6,514 African Americans, 3,062 Native Hawaiians, 4,932 Latinos, 10,680 Japanese Americans, and 9,877 whites. Of the people smoking 21 to 30 cigarettes per day, there were 1,671 African Americans, 1,419 Native Hawaiians, 1,406 Latinos, 4,715 Japanese Americans, and 6,062 whites. Of the people smoking at least 31 cigarettes per day, there were 759 African Americans, 788 Native Hawaiians, 800 Latinos, 2,305 Japanese Americans, and 3,970 whites.

39.

Complete the table.

Smoking level per dayAfrican AmericanNative HawaiianLatinoJapanese AmericansWhiteTotals
1-10
11-20
21-30
31+
Totals

Table 11.26 Smoking Levels by Ethnicity (Observed)

40.

State the hypotheses.
$$H_0$$: _______
$$H_a$$: _______

41.

Enter expected values in Table 11.26. Round to two decimal places.

Calculate the following values:

42.

$$df$$ = _______

43.

$$\chi^2$$ test statistic = ______

44.

Is this a right-tailed, left-tailed, or two-tailed test? Explain why.

45.

Graph the situation. Label and scale the horizontal axis. Mark the mean and test statistic. Shade in the region corresponding to the confidence level.

State the decision and conclusion (in a complete sentence) for the following preconceived levels of \alpha.

46.

$$\alpha = 0.05$$

1. Decision: ___________________
2. Reason for the decision: ___________________
3. Conclusion (write out in a complete sentence): ___________________
47.

$$\alpha = 0.01$$

1. Decision: ___________________
2. Reason for the decision: ___________________
3. Conclusion (write out in a complete sentence): ___________________

### 48.

A math teacher wants to see if two of her classes have the same distribution of test scores. What test should she use?

49.

What are the null and alternative hypotheses for Exercise 11.48?

50.

A market researcher wants to see if two different stores have the same distribution of sales throughout the year. What type of test should he use?

51.

A meteorologist wants to know if East and West Australia have the same distribution of storms. What type of test should she use?

52.

What condition must be met to use the test for homogeneity?

Use the following information to answer the next five exercises: Do private practice doctors and hospital doctors have the same distribution of working hours? Suppose that a sample of 100 private practice doctors and 150 hospital doctors are selected at random and asked about the number of hours a week they work. The results are shown in Table 11.27.

20–3030–4040–5050–60
Private practice1640386
Hospital8445939

Table 11.27

53.

State the null and alternative hypotheses.

54.

$$df$$ = _______

55.

What is the test statistic?

56.

What can you conclude at the 5% significance level?

### 57.

Which test do you use to decide whether an observed distribution is the same as an expected distribution?

58.

What is the null hypothesis for the type of test from Exercise 11.57?

59.

Which test would you use to decide whether two factors have a relationship?

60.

Which test would you use to decide if two populations have the same distribution?

61.

How are tests of independence similar to tests for homogeneity?

62.

How are tests of independence different from tests for homogeneity?