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# Confidence Interval

### Estimating the Mean - Hypothesis Test

If 45 officials in student services earned an average of x(with a line over it) = \$50,340 each year: a. Assume that the standard deviation is 16,920 for salaries of officials. Find the 90% confidence interval for the population mean salary of such personal. What is the margin of error. b. If SD is 10,780, Find the 90% conf

### Test Tires Using a 95% Confidence Interval of Average Mileage

"Joe" is he shop manager at a truck line and is approached by a salesman about some new tires. The salesman assures Joe that the tires will get an average of 60,000 miles before wearing out. Not being that gullible Joe asks for 100 tires for a test. The tires are mounted and run to wear-out and the 95% confidence interval of

### Confidence Intervals, Sample Size, and Confidence Levels

1. Can you give a general rule as to what happens with confidence intervals as a function of sample sizes and confidence levels? What are the trade-offs? 2. Take a sample of something in your work environment, something simple, and calculate a confidence interval. Some possible samples: the average number of people in y

### Statistics: Large Sample Confidence Interval for a Population

The lengths of 225 fish caught in Lake Michigan had a mean of 15.0 inches. Assume that the population standard deviation is 2.5 inches. - Give a point estimate for mu, the population mean . - Find the 90% confidence interval for the population mean length.

### Confidence Interval

In an effort to compare college costs in State of Michigan, a sample of 36 junior students is randomly selected statewide from the private colleges and 36 more from the public colleges. The private college sample resulted in a mean of \$27,650 and the public college sample mean was \$11,360. Assume the annual college fees for priv

### Hypothesis Test: Mean Yearly Sugar Consumption

The American Sugar Producers Association wants to estimate the mean yearly sugar consumption. A sample of 16 people reveals the mean yearly consumption to be 60 pounds with a standard deviation of 20 pounds. A. What is the value of the population mean? What is the best estimate of this value? B. Explain why we need to use th

### T Critical and Confidence Interval

See the attached file. 2) Use Table 4 of the appendix to find tc for a 0.99 confidence level when the sample size is 4. 4) Use Table 4 of the Appendix to find tc for 0.95 confidence level when the sample size is 12. 6) Wildlife: Wolf Pups. The number of pups in the wolf dens of the southwestern United States is recorded b

### How do you construct a confidence interva for the true mean ...

A sample of 20 pages was taken without replacement from the 1,591 phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps and text). The data (in square millimeters) are shown below: 0 260 356 403 536

### Confidence Intervals and Statistics Testings

1. The P-value for a two sided test of the null hypothesis H0: µ = 30 is 0.04. a) Does the 95% confidence interval include the value 30? Why? b) Does the 90% confidence interval include the value 30? Why? 2. The level of calcium in the blood in healthy young adults varies with mean about 9.5 milligrams per deciliter and st

### Exercises of Applied Statistics in Business and Economics

Please complete these 2 exercises from Applied Statistics in Business and Economics. 8.46 A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were 3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477 (a) Construct a 90 percent conf

### Econometrics - Estimate the Mean and Variance

Please see the attached file. Estimate the Mean and Variance....... Calcuate 95 percent confidence........ Do the confidence intervals.......... Do the confidence intervals for average.......

### Confidence interval calculation

1. A quality engineer is responsible for maintaining control of the bottling process in a beer factory. The goals is to maintain the intended volume (6 oz) with as little variation as possible. Since product sampled is not suitable for sale and becomes waste, it is very important to sample a minimal number of bottles. However, i

### Statistics - Confidence Interval Random Sample

Company looked at a random sample of 100 invoices from a large population. Eight of these contain an error. What are the 90% and 95% confidence intervals for the proportion of invoices with errors?

### Confidence Interval for mean.

A machine makes parts with a variance of 14.5cm in length. A random sample of 50 parts has a mean length of 106.5cm. What are the 95% and 99% confidence intervals for the length of parts?

### Standard errors and difference in proportion

1. Find the standard error of the mean for each sampling situation (assuming a normal population). What happens to the standard error each time you quadruple the sample size? a. sigma = 32, n = 4 b. sigma = 32, n = 16 c. sigma = 32, n = 64 2. The American Bankers Association reports that, in a sample of 120 consumer

### Compute confidence interval and test population mean

1. Compute the 95% confidence interval on the population mean if a sample of 1000 is taken and the sample mean is found to be 15.95 and standard deviation is 4.2. Interpret the interval. What does it mean? 2. Test to see if a population mean is greater than the assumed (or historical) value of 16. When a sample of 1000

### Statistics - Confidence Interval Problem

In a comparative study of two new drugs, A and B, 225 patients were treated with drug A and 400 Patients wer treated with drug ......(Please see attached file)

### Statistics: Solving for the Confidence Interval

Question: A sample of 20 pages was taken without replacement from the 1,591 page phone directory Ameritech Pages Plus Yellow Pages. On each page the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below: 0

### Confidence Interval - Biting an unpopped kernel of popcorn

Biting an unpopped kernel of popcorn hurts! As an experiment,a self confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the unpopped kernels were counted. There were 86. a) Construct a 90% confidence interval for the proportion of all kernels that would not pop b) Che

### Finding confidence interval for true mean

Find the confidence interval for the true mean assuming that each sample is from a normal population and we know the standard deviation: The given data is: Xbar = 14 Standard deviation = 4 N=5 Use the 95% confidence level.

### Statistics: Determining the Confidence Interval

Scenario: A random sample of 10 miniature Tootsie Rolls were taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were as follows: 3.087, 3.131, 3.241, 3.41, 3.70, 3.353, 3.400, 3.411, 3.437, 3.477 Questions: a) Construct a 90% confidence interval for the true mean weight. b) What sa

### Confidence Interval - In, 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security related jobs, and found that 1,143 were positive. ...

In, 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security related jobs, and found that 1,143 were positive. a) Construct a 95% confidence interval for the population proportion of positive drug tests b) Why is the normality assumption not a problem, despite

### Statistical survey - Ms. Maria Wilson is considering running for mayor of the town of Bear Gulch, Montana. Before completing the petitions, she decides to conduct a survey of voters in Bear Gulch. A sample of 400 voters reveals that 300 would support her in the November election. ...

Ms. Maria Wilson is considering running for mayor of the town of Bear Gulch, Montana. Before completing the petitions, she decides to conduct a survey of voters in Bear Gulch. A sample of 400 voters reveals that 300 would support her in the November election. a. Estimate the value of the population proportion. b. Compute the

### Statistics - Confidence Interval..

Please help with following problems & show how to do work in excel or megastat. 8.60 A certain brand of dry noodles contains a mixture of beet, spinach, carrot, and plain. A random sample of 200 dry noodles contained 47 beet noodles. (a) Construct a 95 percent confidence interval for the true proportion of beet noodles. (b)

### Confidence Interval

What does it mean when you apply confidence intervals using a normal distribution?

### Statistics - Confidence Interval

When 500 college students are randomly selected and surveyed, it is found that 135 of them own personal computers (based on data from the America Passage Media Corporation). A. Find the point estimate of the true proportion of all college students who own personal computers. B. Find a 95% confidence interval for the tru

### Significance Tests and Confidence Intervals

Please help with the following problem. Using the data on the table below, are there any correlations between population changes for the areas listed. The following is a list of acceptable tests: regression line and equation; correlation one-sample t-test one-sample t confidence interval matched-pairs t-test two-sa

### Hypothesis Testing With a 95% Confidence Interval for Mean

We have created 95% confidence interval for mean; with the result (10, 15). What decision will we make if we test H0 : mean = 16 versus H1 : mean is not equal to16 at alpha = 0.025? Reject H0 in favor of H1. Accept H0 in favor of H1. Fail to reject H0 in favor of H1. We cannot tell what our decision will be from the inform

### 90% confidence level - A dean of a business school wanted to know whether the graduates of her school used a statistical inference technique during their first year of employment after graduation. She surveyed 314 graduates and asked about the use of statistical techniques. After tallying up the responses, she found that 204 used statistical inferences within 1 year of graduation. Estimate with 90% confidence the proportion of all business school graduates who use their statistical education within a year of graduation.

A dean of a business school wanted to know whether the graduates of her school used a statistical inference technique during their first year of employment after graduation. She surveyed 314 graduates and asked about the use of statistical techniques. After tallying up the responses, she found that 204 used statistical inferen

### Increasing the Precision of the Confidence Interval

1. What is the most controllable method of increasing the precision (narrowing) of the confidence interval? 2. What percentage of times will the mean (population proportion) not be found within the confidence interval? 3. When you draw a sample from a normal distribution, what can you conclude about the sample distribution? Ex