Ashford BUS308 Week 3 Chapter 11 Assignment

Question 1

Stable cost reporting in a manufacturing setting is typically a sign that operations are running smoothly. The accounting department at Rockwell Collins, an avionics manufacturer, analyzes the variance of the weekly costs reported by two of its production departments. A sample of cost reports for each of the two departments shows cost variances of and , respectively. Is this sample sufficient to conclude that the two production departments differ in terms of unit cost variance? Use (to decimals).

Question 2

The competitive advantage of some small American factories such as In Tolerance Contract Manufacturing lies in their ability to produce parts with very narrow requirements, or tolerances, that are typical in the aerospace industry. Consider a product with specifications that call for a maximum variance in the lengths of the parts of . Suppose the sample variance for parts turns out to be . Use , to test whether the population variance specification is being violated.

: Test statistic = (to 2 decimals, if required)

The -value is

. Use Table 11.1.

Question 3

In its Auto Reliability Survey, Consumer Reports asked subscribers to report their maintenance and repair costs. Most individuals are aware of the fact that the average annual repair cost for an automobile depends on the age of the automobile. A researcher is interested in finding out whether the variance of the annual repair costs also increases with the age of the automobile. A sample of automobiles years old showed a sample standard deviation for annual repair costs of and a sample of automobiles years old showed a sample standard deviation for annual repair costs of .

a. State the null and alternative versions of the research hypothesis that the variance in annual repair costs is larger for the older automobiles. Let year old automobiles be represented by population .

b. At a level of significance, what is your conclusion?

Calculate the value of the test statistic (to decimals).

The -value is

. Use Table 4 of Appendix B.

that year old automobiles have a larger variance in annual repair costs compared to year old automobiles.

Question 4

The variance in a production process is an important measure of the quality of the process. A large variance often signals an opportunity for improvement in the process by finding ways to reduce the process variance. Jelly Belly Candy Company is testing two machines that use different technologies to fill three pound bags of jelly beans. The file Bags contains a sample of data on the weights of bags (in pounds) filled by each machine.Conduct a statistical test to determine whether there is a significant difference between the variances in the bag weights for the two machines. Use a level of significance. What is your conclusion? Which machine, if either, provides the greater opportunity for quality improvements? Click on the datafile logo to reference the data.

(to decimals)

(to decimals)

(to decimals)

 

Question 5

Battery life is an important issue for many smartphone owners. Public health studies have examined "low-battery anxiety" and acute anxiety called "nomophobia" that results when a smartphone user's phone battery charge runs low and then dies (Wall Street Journal, May , ). Battery life between charges for the Samsung Galaxy S9 averages hours when the primary use is talk time and hours when the primary use is Internet applications. Because the mean hours for talk time usage is greater than the mean hours for Internet usage, the question was raised as to whether the variance in hours of usage is also greater when the primary use is talk time. Sample data showing battery life between charges for the two applications follows. Click on the datafile logo to reference the data.

Primary Use: Talking
	35.8		22.2		24.0		32.6		18.5		42.5
	28.0		23.8		30.0		22.8		20.3		35.5
Primary Use: Internet
	14.0		12.5		16.4		11.9		9.9		3.1
	5.4		11.0		15.2		4.0		4.7

a. Formulate hypotheses about the two population variances that can be used to determine whether the population variance in battery life is greater for the talk time application. Consider the talk time use as population and Internet use as population .

b. What are the standard deviations of battery life for the two samples (to decimals)?

c. Conduct the hypothesis test and compute the -value.

p-value = (to decimals)

Using a level of significance, what is your conclusion?

. We

that the population variance in battery hours of use for the talk time application is larger than the population variance in battery hours of use for the Internet application.

Question 6

According to the Corporate Travel Index compiled by Business Travel News, the average daily cost for business travel in the United States rose to per day (Executive Travel website). The file Travel contains sample data for an analogous study on the estimated daily living costs for an executive traveling to various international cities. The estimates include a single room at a four-star hotel, beverages, breakfast, taxi fares, and incidental costs. Click on the datafile logo to reference the data.

City	Daily Living Cost ($)	City	Daily Living Cost ($)
Bangkok	242.87	Mexico City	212.00
Bogota	260.93	Milan	284.08
Cairo	194.19	Mumbai	139.16
Dublin	260.76	Paris	436.72
Frankfurt	355.36	Rio de Janeiro	240.87
Hong Kong	346.32	Seoul	310.41
Johannesburg	165.37	Tel Aviv	223.73
Lima	250.08	Toronto	181.25
London	326.76	Warsaw	238.20
Madrid	283.56	Washington, D.C.	250.61

a. Compute the sample mean (to decimals).

b. Compute the sample standard deviation (to decimals).

c. Compute a confidence interval for the population standard deviation (to decimals). Use Table 11.1.

( , )

Question 7

Is there any difference in the variability in golf scores for players on the LPGA Tour (the women's professional golf tour) and players on the PGA Tour (the men's professional golf tour)? A sample of tournament scores from LPGA events showed a standard deviation of strokes, and a sample of tournament scores from PGA events showed a standard deviation of . Conduct a hypothesis test for equal population variances to determine whether there is any statistically significant difference in the variability of golf scores for male and female professional golfers. Use .

What is your conclusion?

There is

significant difference in the variances.

 

Question 8

Stable cost reporting in a manufacturing setting is typically a sign that operations are running smoothly. The accounting department at Rockwell Collins, an avionics manufacturer, analyzes the variance of the weekly costs reported by two of its production departments. A sample of cost reports for each of the two departments shows cost variances of and , respectively. Is this sample sufficient to conclude that the two production departments differ in terms of unit cost variance? Use (to decimals).