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# Confidence Interval

### Confidence interval for the population mean

A corporation that maintains a large fleet of company cars for the use of its sales staff is interested in the mean distance driven monthly per sales person. The following table gives the monthly distances in miles driven by a random sample of 20 sales persons 2314, 2102, 1999, 1951, 2602, 2468, 1881, 2381, 2230, 1966, 2246, 26

### Confidence interval estimation and sample size

At a large department store, the average number of years of employment for a cashier is 5.7 with a standard deviation of 1.8 years. If the number of years of employment at this department store is normally distributed, what is the probability that a cashier selected at random has worked at the store for over 10 years? A) 0.4

### 90% and 99% Confidence interval for HMO example

A random sample of 19 HMO's was selected. For each HMO the co-payment for a doctors office visit was recorded. The results were... In dollars, 9,10, 11, 10, 7, 6, 5, 12, 11, 10, 12, 8, 7, 6, 11, 6, 8 Under the assumption that co payment amounts are normally distributed, find a 99% confidence interval for the mean amount

### Confidence Interval, Normality Assumption & Very Quick Rule

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 percent confidence interval for the proportion of all kernels that would not po

### Constructing confidence intervals using data

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: 0 260 356 4

### The upper limit of a 95% confidence interval for the population mean would equal? If the 10% level of significance ws used in testing the hypthesis H1o:u=201, H1" u = 201 the null hypothesis:

1) A random sample of size 15 taken from a normally distributed population revealed a sample mean of 75 and a sample variance of 25. The upper limit of a 95% confidence interval for the population mean would equal? 2. Based on sample data the 90% confidence interval limits forth population mean are 170.86 and 195.42. I

### Statistics - Confidence Intervals and Standard Deviation

Please help with the following problems. Provide step by step calculations. 1. The security department of a university is planning its budget for the next year. in estimating the man-hours for security during university sponsored music concerts, the average length of music concerts is needed. A random sample from 36 secur

### Phone Directory, Kettle Corn

8.48 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: 0 260

### Statistics Confidence Interval

A sample of 40 investment customers serviced by an acct manager are found to have had an average of #23,000 in transactions during the past year, with a standard deviation of \$8,500. A sample of 30 customers serviced by another account manager averaged \$28,000 in transactions, with a standard deviation of \$11,000. Assuming the

### Home Sales, Bedroom Size, Floor Size

Data collected from the sale of 105 homes .The table shows that the majority of the homes sold. The table illustrates that 72% of the homes sold were four bedrooms or less. The data also demonstrates that the majority of homes sold are below 2400 square feet.

### Confidence interval for a population proportion

A genetic experiment with peas resulted in one sample of offspring that consisted of 438 green peas and 159 yellow peas. A. 90 % Confidence intervals to estimate the percentage of yellow peas would be? B. It was expected that 25% of the offspring peas would be yellow. Given that percentage of offspring yellow peas is not

### From a production line A, a sample of 200 items is selected at random; and it is determined that 16 items are defective ...

From a production line A, a sample of 200 items is selected at random; and it is determined that 16 items are defective. While in a sample of 300 items from production process B (which produces identical items to line A) there are 21 defective items. Determine a 95% confidence interval estimate for the difference between the pro

### Understanding confidence intervals

What do we mean by confidence intervals - provide an example that illustrates your answer. Suppose we were to apply 95% and 99% confidence to your study results.. how might your result differ and why?

### Confidence Interval - In most cities a municipal agency regulates the amounts charged by taxis. Total taxi fares are determined by distance traveled as well as the ...

In most cities a municipal agency regulates the amounts charged by taxis. Total taxi fares are determined by distance traveled as well as the amount of time taken for the trip. In preparing to apply for a rate increase the general manager of a taxi fleet wanted to know the distance customers travel by taxis on the average trip.

### Confidence interval for proportion

An airline has surveyed a simple random sample of air travelers to find out whether they would be interested in paying a higher fare in order to have access to e-mail during their flight. Of the 400 travelers surveyed, 80 said email access would be worth a slight extra cost. Construct a 95% confidence interval for the populati

### Calculations with confidence interval for mean

Please help with the following problems. 1. For df = 25, determine the value of A that corresponds to each of the following probabilities: a.P(t > A) = 0.25 b. P( < A) = 0.10 c. P(-A < t < A) = .99 2. Given the following observations in a simple random sample from a population that is approximately normally distrib

### Interval Estimate

During the month of July, an auto manufacturer give tis production employees a vacation period so it can tool up for the new model run. In surveying a simple random sample of 200 production workers, the personnel director finds that 38% of them plan to vacation out of state for at least one week during this period. Is this a p

### Confidence interval for proportion ..

In response to media inquiries an dconcerns expressed by groups opposed to violence, the president of a university with over 25,000 students has agreed to survey a simple random sample of her students to find out whether the student body thinks the school's "Plundering Pirate" mascot should be changed to one that is less aggress

### Confidence Interval for mean

An assembly process inlcudes a torque wrench device that automatically tightens compressor housing bolts; the device has a known process tandard deviation of o = 3 lb-ft in the torque applied. A simple random sample of 35 nuts is selected, and the average torque to which they have been tightened is 150 lb-ft. What is the 95%

### Confidence intervals and means

The mean number of travel days per year for the outside salespeople employed by hardware distributors is to be estimated. The 0.90 degree of confidence is to be used. The mean of a small pilot study was 150 days, with a standard deviation of 14 days. If the population mean is to be estimated within two days, how many outside sal

### Confidence Intervals and One-Sample Hypothesis Test

See attachment for fully formatted question. ----------------------------------------------------------------- Confidence Intervals and One-Sample Hypothesis Test 1. Collect data. Develop a 90% confidence interval and a 95% confidence interval for the population mean. Did you use a z statistic or t statistic? Why? Compare

### Confidence Intervals, Hypothesis Testing, and Testing Errors

In a study to determine the impact of parental involvement on student achievement, 127 seniors in a suburban high school were surveyed. Students were asked to report their ACT scores and answer a series of questions about their parent's involvement in their education. Of the 127 students, 91 reported high parental involvement an

### Student Earnings: Confidence intervals and margins of error

6. Salaries: Student services consider college officials in admissions, registration, counseling, financial aid, campus ministry, food service, and so on. How much money do these people make each year? Suppose you read in your local newspaper that 45 officials in student services earned an average of = \$50,340 each year. a

### Sample size calculation

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 processor of carrots cuts the green top off each carrot, washes the carrots, and inserts six to a package. Twenty pa

### Sample Population Confidence Intervals Case Study

1. Collect data. Develop a 90% confidence interval and a 95% confidence interval for the population mean. Did you use a z statistic or t statistic? Why? Compare the size and meaning of the two confidence intervals. 2. Take a random sample and test a hypothesis about a population mean. Explain what assumptions you made.

### Statistics - Hypothesis Test - Confidence Interval

Problem: A new product was test marketed in the Des Moines, Iowa, and Toledo, Ohio, metropolitan areas. Advertising in the Des Moines area was done entirely on television, while adverising in the Toledo area consisted of a mixture of television, radio, newspaper and magazine ads. Two months after the advertising campaigns com

### Estimation

Select the correct answer and write the appropriate letter in the space provided. ______ 1. A single number used to estimate a population parameter is a. the confidence interval. b. the population parameter. c. a point estimate. d. the mean of the population. ______ 2. A range of values constructed from sample data so

### Use Excel to Construct Confidence Intervals

See the attached file. Please help in setting up and solving the problem given below. The problem with necessary data is fully set up in the attached Excel document. INSTRUCTION: Include a "summary statement" for each CI. Use the data for which is given in columns A:C. FACTS / PROBLEM: USE EXCEL AND EXCEL FUNCTIONS

### Find the confidence interval for a population proportion.

Confidence Interval I need help setting up and solving a confidence interval problem. The problem is set out below and is set out in the attached excel spread sheet. INSTRUCTION: Include a "summary statement" for each CI. PROBLEM: Find a 69% CI for the population proportion of successes when a sample of 57 had 32

### Data Analysis - Finding Sample Sizes for Confidence Intervals

INSTRUCTIONS: Include a "summary statement" for each CI. FACTS: Elected officials in a small Florida town are preparing for the annual budget for their community. Specifically, they would like to estimate how much their constituents living in this town are typically paying each year in real estate taxes. Given that the