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# Confidence Interval

### Statistical Techniques in Business: Ch 9, 34, survey of 50 executives laid off

Chapter 9, 34 A recent survey of 50 executives who were laid off from their previous position revealed it took a mean of 26 weeks for them to find another position. The standard deviation of the sample was 6.2 weeks. Construct a 95 percent confidence interval for the population mean. It is reasonable that the population mean

### Hypothesis Testing & Confidence Intervals

Question: A survey of 100 mayonnaise purchasers showed 65 were loyal to one brand. Whereas a survey of 100 bath soap purchasers showed only 53 were loyal to one brand. a) Perform a two tailed test at alpha = .05 b) Form a confidence interval for the difference of proportions, without pooling the samples. Does it include 0?

### Construct a 95% Confidence Interval

A random sample of 85 group leaders, supervisors, and similar personnel at General Motors revealed that, on the average, they spent 6.5 years on the job before being promoted. The standard deviation of the sample was 1.7 years. Construct a 95 percent confidence interval.

### Confidence Interval and Hypothesis Test

1. A sample of 35 golfers showed that their average score on a particular golf course was 80 with a standard deviation of 6. Answer each of the following (show all work): (A) Find the 95% confidence interval of the mean score for all 35 golfers. (B) Find the 95% confidence interval of the mean score for all golfers if this

### Fashion Industries: Applicants Condition of Employment

As a condition of employment, Fashion Industries applicants must pass a drug test. Of the last 220 applicants 14 failed the test. Develop a 99 percent confidence interval for the proportion of applicants that fail the test. Would it be reasonable to conclude that more than 10 percent of the applicants are now failing the test? I

### Confidence Interval and Standard Deviation: Wage Example

In a random variable of 100 workers you find the average wage is \$21.00 per hour and the standard deviation of wage is \$4.00 per hour. What is the 99% confidence interval for mean hourly wages? (Note that with n=100 Pr (t.2.364)=0.01 and Pr (t>2.626)=0.005

### Confidence Interval for Customer Satisfaction and Testing

Quality Progress, February 2005, reports on the results achieved by Bank of America in improving customer satisfaction and customer loyalty by listening to the voice of the customer. A key measure of customer satisfaction is the response on a scale from 1 to10 to the question: Considering all the business you do with Bank of

### Confidence Interval & Sample Size for a Random Sample

1 (b). A survey of a random sample of 250 car commuters indicates that 80 would switch to commuting by public transport if they had to pay at least \$10 per week for parking at their work places. (i) Using a 95% confidence level, calculate the confidence interval for the proportion of the commuters who might be expected to ch

### Statistics: Confidence Interval for Mean

* The UNITE/MORI 2004 survey of student experiences estimated that university students in the UK paid on average \$54 per week in accommodation costs. Assume that this average is based on a sample 755 students and that the population standard deviation for weekly accommodation costs is \$ 11. a. Construct a 90 per cent confi

### Confidence Interval: Proportion of Drug Test

As a condition of employment, Fashion Industries applicants must pass a drug test. Of the last 220 applicants 14 failed the test. Develop a 99 percent confidence interval for the proportion of applicants that fail the test. Would it be reasonable to conclude that more than 10% of the applicants are now failing the test? In addit

### Assessing Sample Size for the Number of "Walk-Ins"

Part of my job description is to teach Recruiters their daily individual tasks and how to properly manage their time. One of the Recruiter duties is to generate appointments in many different ways. They can visit high schools, Shopping Centers, or any other public places available within their Recruiting zone; their main goal

### Confidence Interval

1. In each of the following exercises, a set of condition is given. To construct a 95 percent confidence interval for the population mean, would you use the z distribution, a t distribution, or neither? Where appropriate, determine the z or t value. n = 21, xbar = 23.1, s = 7.5, population distribution shape normal, &#963; = 7.

### Confidence interval

A machine produces 9 inch latex gloves. A sample of 85 gloves is selected, and it is found that 36 are shorter than they should be. Find the 98% confidence interval on the proportion of all such gloves that are shorter than 9 inches

### Find confidence interval

Use the given degree of confidence and sample data to find a confidence interval for the population standard deviation o. Assume that the population has a normal distribution. Weights of men: 90% confidence; n=14, Xbar=160.9lb, s=12.6lb

### Construct a 98% confidence interval for the Mean

The amounts (in ounces) of juice in eight randomly selected juice bottles are: 15.0 15.9 15.3 15.3 15.5 15.9 15.9 15.0 Construct a 98% confidence interval for the mean amount of juice in all such bottles.

### Constructing a 95% Confidence Interval: Public Transportation

A sociologist develops a test to measure attitudes about public transportation, and 27 randomly selected subjects are given the test. Their mean score is 76.2 and their standard deviation is 21.4. Construct the 95% confidence interval for the mean score of all such subjects.

### Construct a confidence interval for the population proportions

Of 346 items tested, 12 are found to be defective. Construct the 98% confidence interval for the proportion of all such items that are defective. How do you convert the numbers to equate like this: 0.0345<p<0.0349

### Construct a Confidence Interval for the Population Proportion P

A survey of 300 union members in New York reveals that 112 favor the Republican candidate for governor. Construct the 98% confidence interval for the true population proportion of all New York State union members who favor the Republican candidate.

### Statistic

Week 8: ________________________________________ There are 2 pages in this exam. Be sure to complete all pages before submitting the exam. Page: 1 2 ________________________________________ Time Remaining: 1. (TCO 9) What is the feasible range for r, the correlation coefficient? (Points: 6) 0 to 1

### Average Hemoglobin Readings for Sample of Teachers

The average hemoglobin reading for a sample of 35 teachers was 16gr/milliliters, with a sample standard deviation of 2 grams. Find the 99% confidence interval of the true population mean. Provide an interpretation of the interval.

### Confidence Interval: Nursing school alumi & Auditor for bank

A nursing school wants to estimate the true mean annual income of its alumni. It randomly samples 200 of its alumi. The mean annual income was 55,200 with a standard deviation of 1,500. Find the 95% confidence inteval for the true mean annual income of the nursing school alumni. 2. An auditor wants to estimate what proporti

### Confidence Interval for Students Promotion

A random sample of 42 college graduates who worked during their program revealed that a student spent an average 5.5 years on the job before being promoted. The sample standard deviation was 1.1 years. Using the 0.99 degree of confidence, what is the confidence interval for the population mean? A. 5.04 and 5.96 B. 5.06 and 5.

### Statistics

() is a pi symbol. 2. In the next presidential election of year 2012, five candidates running for the election are Sarah Palin, Hilary Clinton, Barack Obama, Mitt Romney, and Rudy Giuliani. It is desired to estimate the true proportion ( ) favoring one of the five candidates. a) based on sample size 1000 with 92% confidence,

### Confidence Interval for ISO Certification

In a random sample of 100 manufacturing firms, 67 indicated that their company attained ISO certification within the last two years. Find a 95% confidence interval for the population proportion of companies that have been certified within the last two years. In solving the above question you must write the formula of the confide

### Statistics

Statistics 2 1) Northeastern University (NU) wants to determine if its students spend more time studying than do students attending Boston University (BU). Random samples of 9 students are taken at BU and NU. The two samples reveal the following data: Daily hours studying at NU 6 3 0 3 6 0 2 3 4 Daily hours st

### Confidence Interval for Pulse Rate Increase

A certain medication is known to increase the pulse rate of its users. The variance of the pulse rate is known to be 10 beats per minute. A sample of 32 users had an average pulse rate of 104 beats per minute. Find the 99% confidence interval of the population mean. Provide an interpretation of the confidence interval.

### Statistics: probability, confidence interval, mean, standard deviation, test statistic

See attached four problems. Please show all work and please follow all instructions. 1. Avery short quiz has one multiple choice questions with five possible choices (a, b, c, d, e) and one true or false question. Assume you are taking the quiz but do not have any idea what the correct answer is to either question, but you

### Statistics: finding correct z and t scores for confidence intervals

Finding appropriate z- and t-scores is important when constructing confidence intervals. Confidence intervals allow one to estimate important population parameters such as population mean, population proportion, population standard deviation, etc. We will also study how confidence intervals will let one determine how large of

### SPSS Confidence Intervals and Chi-Squared: Example Problems

Assume you are the manager of a mustard seed factory in Colombia. Your company has received complaints that there is not enough mustard seed in your economy size packages. You ask your supervisor and chief operating officer Juan Valdez to test the new mustard seed packaging machine you are installing. He runs a sample of 36 pac

### Confidence Interval estimation and interpretation.

Of 43 bank customers depositing a check, 18 received some cash back. (a) Construct a 90% confidence interval for the proportion of all depositors who ask for cash back. (b) Check the normality assumption.