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# Confidence Interval

### Analyze business decision opportunities using basic inferential statistics.

use the Confidence Interval Calculator and the Area Gas Prices - Random Sample Excel file The Minneapolis Star Tribune newspaper has decided to write an article about gasoline prices in the Twin Cities area (Minneapolis and St. Paul). The paper has designed a survey and taken a simple random sample of regular, unleaded gas pr

### Confidence Interval Estimate for the Mean

Question 1 Sample with size n = 100 has mean = 30. Assuming the population standard deviation is 8, construct 95% confidence interval for population mean. Use formula on page 312, z?/2 = 1.96 Answer between 28.4 and 31.6 between 27.0 and 33.0 between 26.1 and 34.2

### Confidence Interval and Margin of Error

In an effort to estimate the mean amount spent per customer for dinner at a major Atlanta restaurant, data were collected for a sample of 49 customers. Assume a population standard deviation of \$5. a. At 95% confidence, what is the margin of error? b. If the sample mean is \$24.80, what is the 95% confidence interval for th

### Sample Size & Normal Probability..

There are two problems attached. One asks you to calculate How many replicates are need within 95% confidence. Unknown mean and known SD The other I believe is asking for z scores but not sure how n affects these values

### Driving Habits of Individuals-Confidence Interval for Speed

The Highway Safety Department wants to study the driving habits of individuals. A sample of 81 cars travelling on the highway revealed an average speed of 67 miles per hour with a sample standard deviation of 9 miles per hour. Construct a 99% confidence interval estimate for the speed of all cars.

### Confidence Intervals for School Planners

A school planner is interested in determining the proportion of spring semester students that will attend summer school. She takes a sample of 160 spring semester students discovering that 56 will return to summer school. Construct a 98% confidence interval estimate for the proportion of spring semester students who will retu

### Confidence Intervals

Random sampling from two normal populations produced the following results: Xbar1= 63, s1= 18 n1=50 xbar2= 60 s2 = 7 n2 = 45 a. Estimate with 90% confidence the difference between the two population means. b. Repeat part a changing the sample standard deviations to 41 and 15 respectively. c. What happens when the s

### Sample Size & Confidence Interval

1. The library New York City Public Library asked assistant interval estimate number books checked day. The assistant a sample found 880 books. The librarian interval estimate 790 970 books checked day. Which efficient unbiased point estimate number books checked day New York City Public Library is? 2. A researcher dean wou

### Confidence Intervals and Sample Size Problems

1) Eight chemical elements do not have isotopes (different forms of the same element having the same atomic number but different atomic weights). A random sample of 30 of the elements that do have isotopes showed a mean number of 19.63 isotopes per element and the population a standard deviation of 18.73. Estimate the true

### MBA statistics-Confidence Interval Estimate

Difficult to comprehend. Many need to be in Excel format to answer. 1. What proportion of Americans get most of their news from the internet? According to a poll conducted by Pew Research Center, 40% get most of their news from the Internet. a. To conduct a follow-up study that would provide 95% confidence that the point es

### MBA statistics-Confidence Interval Estimate

Difficult for me to comprehend! Several need to be answered with Excel. 1. If sample mean = 85, and n=64, construct a 95% confidence interval estimate for the population mean, mu. 2.The manager of a paint supply store wants to estimate the actual amount of paint contained in 1-gallon cans purchased from a nationally known

### Quantative Analysis

A corporation owns several companies. The strategic planner for the corporation believes dollars spent on advertising can to some extent be a predictor of total sales dollars. As an aid in long-term planning, she gathers the followings sales and advertising information from several of the companies for 2002 (\$ millions). Adve

### Confidence interval for mean

Word-process formulas using Equation Editor and diagrams using Drawing Tool. Annual family dental expenses for the families of a random sample of ten employees of a company are given below. You can assume the family dental expenses for the employees of the company are normally distributed. \$450, \$390, \$550, \$140, \$690, \$6

### Point and interval estimate and efffect size

Brian I have two questions for you. I hope you can help. 1. What is the difference between a point estimate and an interval estimate? How would you calculate a confidence interval with a z test? 2. What is an effect size, and why would reporting it be useful?

### confidence intervals

Generate 50 random samples of size 10 from the file MBA and compute a 90% confidence interval for the mean of for each sample using the known population standard deviation of 3.831. Determine how many confidence intervals actually contain the true population mean of 14.77

### Use of stratified random sampling; statistical control

1. When is it appropriate to use stratified random sampling. 2. What is meant when we say that a process is in statistical control? 3. Discuss ratio, interval, nominal and ordinal variables. 4. Explain what is meant by a margin of error for a confidence interval.

### Statistics: Confidence Interval problems

See attached data file. #1. 8.15: Using Table A.4 (page 640), find t.100, t.025, and t.001 based on 11 degrees of freedom. Also, find these t points based on 6 degrees of freedom. #2. 8.16: Suppose that for a sample of n = 11 measurements, we find that _ = 72 and s 5. Assuming normality, compute confidence intervals

### Testing Procedure, p-Value and Confidence Interval

The mean + sd of In [calcium intake (mg)] among 25 females, 12 to 14 years of age, below the poverty level is 6.56 + 0.64. Similarly, the mean + 1 sd of In [calcium intake (mg)]among 40 females, 12 to 14 years of age, above the poverty level is 6.80 + 0.76. 8.3) What is the appropriate procedure to test for a significant diff

### Statistics problems: Confidence interval, population mean, level of significance, error, regression model

1. The union representing the Bottle Blowers of America (BBA) is considering a proposal to merge with the Teamsters Union. According to BBA union bylaws, at least three-fourths of the union membership must approve any merger. A random sample of 2,000 current BBA members reveals 1,600 plan to vote for the merger proposal. What is

### Estimate the difference in the proportion of morning

A supermarket chain wants to determine the difference the proportion of morning shoppers who are man and the proportion of evening shoppers who are men. A random sample of 400 morning shoopers showed that 48 were men. A random sample of 480 evening shoppers showed 187 were men. Constuct and explain a 95% confidence interval e

### Hypothesis at a 95% confidence interval for mean weight

A quality control engineer wanted to estimate the mean weight (in grams) of M&M candies being produced on a certain machine in the factory. After collecting an appropriate random sample of M&M candies, he obtained the following weights: .81 .86 .85 .79 .98 .84 .9 .87 .77 .82 .86 .87 .87 .88 .94 .86 .96 .82 .88 .98 .75 .

### Confidence interval to test proportion of US households with a dog

A humane society claims that less than 35% of U.S. households own a dog. In a random sample of 400 U.S. households, 156 say they own a dog. (5) Describe the population of interest and calculate the numerical value of the statistic p Ì? that that we will use to estimate the population proportion p. (5) Construct a 95% c

### Interval Estimation & Margin of Error

# 1. use the sample data and confidence level to construct the confidence interval estimate of the population proportion p. n= 550, x= 440, 95% confidence < p < #2 use the given confidence level and sample data to find (a) the margin of error and (b) the confidence interval for the population mean m. assume that t

### Confidence Interval, Normal Probability & Hypothesis Testing

#4. you collected the following information: n=38 x bar= 12.35 s=3.82 find the 95% confidence interval estimate for m- mule #2. heavy duty light bulbs made by a certain company claim to have lives that are normally distributed with a mean of 5000 hours and a standard deviation of 400 hours. A. find the pr

### Management Science

The number of staff personnel needed to handle patients at a medical center is determined by the mean time that patients must wait before being attended to by a physician. For a random sample of 100 previously recorded emergencies, the sample mean waiting time was 72 minutes, with a standard deviation of 28 minutes. a. wh

### 95% Confidence Interval of the Population Mean Age

In a study of 10 insurance sale representatives from a certain large city, the average age group was 48.6 years and the standard deviation was 4.1 years. Assume the variable is normally distributed. Find the 95% confidence interval of the population mean age of all insurance sales representatives in the city.

### ANOVA and SPC

Need help on the following problems (1) Freshman 15 Weight gains. (Attached Data set 3) Based on the sample results, find the best point estimate of the percentage of college students who gain weight in their freshman year. a. Construct a 95% confidence interval estimate of the percentage of college students who gain wei

### Confidence Interval Concepts

How is the confidence level determined? Who in your workplace might set this level? Should companies use the same confidence interval each time a confidence interval is determined or should the level change based on situations? If it changes based on situations, what type of situations might call for higher confidence levels?

### Linear Regression Model: Midterm Exam vs. Final Exam

Please show detailed calculations. Much appreciated. The following shows the mid-term and final examination scores of a class of 20 statistics students: Midterm Exam. x Final Exam. y 68 75 49 63 60 57 68 88 97 88 82 79 59 82 50 73 73 90 39 62 71 70 95 96 61 76 72 75 87 85 40 40 66 74 58 70 58 75 77 72

### Confidence interval for mean

a random sample of 50 engineers of a large technology company that the sample mean is 34.4 year. assume that the population standard deviation is 8 years. construct and explain a 98% confidence interval estimate of the average age of all engineers employed by the company.