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# Confidence Interval

### Statistics - Confidence Interval for Random Sample

A random sample of 10 shipments of stick-on labels showed the following order sizes. (a) Construct a 95% confidence interval for the true mean order size. (b) How could the confidence interval be made narrower? (c) Do you think the population is normal? Order Size 12,000 18,000 30,000 60,000 14,000 10,500 52,000

### Population mean

Please post on excel. 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. Is it reasonable that the populat

### Statistics Confidence Intervals for color of M&M candies

See attached files. Confidence intervals for the proportion of each color as well as the mean total number of candies per bag. You will use the methods of 6.3 for the proportions and 6.1 for the mean. For the Bonus, you will use the sample size formula on page 338. Please keep at least 4-6 decimal places for the sample pro

### Statistics: Degrees of freedom, sampling error, interval estimate

1. A researcher conducts a two tailed two sample t test on 28 subjects (14 subjects in each Group) and finds that t=1.986. a. How many degrees of freedom are there in this study? b. Estimate the actual type 1 error for this study. c. If the researcher decides to reject the null hypothesis, how confident can the researche

### Statistics: Fashion Industries job applicants must pass a 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 percent of the applicants are now failing the test? I

### Sample size for Families USA estimate of population mean yearly health care premiums

Families USA, a monthly magazine that discusses issues related to health and health costs, surveyed 20 of its subscribers. It found that the annual health insurance premiums for a family with coverage through an employer averaged \$10,979. The standard deviation of the sample was \$1,000. a. Based on this sample information,

### Families USA surveyed subscribers for annual health insurance premiums; sample size

Families USA, a monthly magazine that discusses issues related to health and health costs, surveyed 20 of its subscribers. It found that the annual health insurance premiums for a family with coverage through an employer averaged \$10,979. The standard deviation of the sample was \$1,000. a. Based on this sample information, de

### Confidence interval and sample size.

A manufacturer wishes to estimate the reliability (in months) of a certain product. An estimate of the population standard deviation from a previous sample was 12 months. If the manufacturer desires to be within 4 months of the true value with approximately 80% confidence, what should the sample size be?

### Determining Maximum Error of Estimate: Example Problem

A random sample of size of 25 taken from a normally distributed population yielded a sample variance of 2.25. What is the value for the maximum error of estimate for a 90% confidence interval for the population mean?

### Statistics: Confidence Intervals for M&M candy colors in a bag.

See attached data files. Confidence intervals for the proportion of each color as well as the mean total number of candies per bag. You will use the methods of 6.3 for the proportions and 6.1 for the mean. For the Bonus, you will use the sample size formula on page 338. Please keep at least 4-6 decimal places for the sampl

### Construction of confidence intervals and proper interpretation

Confidence Intervals: A confidence interval is simply a finite interval of score values on the dependent variable. Such an interval is constructed by adding a specific amount to the computed statistic (thereby obtaining the upper limit of the interval) and by the subtracting a specific amount from the statistic (thereby obtainin

### Confidence interval for proportion

A large supermarket conducted a consumer preference study by recording the brand of wheat bread pruchased by customers in its stores. The supermarket carries four brands of wheat bread and the brand preferences of a random sample of 200 purchasers are given in the following table: BRAND A=51 B=82 C=27 D=40 Test the null

### Statistics: Confidence Intervals

Confidence intervals are used to help you get a better feel for your estimated value. Confidence intervals are like nets. You don't know what the TRUE proportion value is so you throw a net (find a confidence interval based upon a survey). The confidence level indicates the percentage of times your net would "catch" the true pop

### Confidence interval for a population proportion

The lifetime of a certain brand of battery is known to have a standard deviation of 11.3 hours. Suppose that a random sample of 90 such batteries has a mean lifetime of 33.4 hours. Based on this sample, find a 95% confidence interval for the true mean lifetime batteries of this brand. What is the lower limit of the 95% confidenc

### Statistics: 12 problems: joint probability, expected value, binomial, sample size (See attached file).

DESCRIPTIVE STATISTICS: The following unsorted data shows the number of traffic tickets given each day by ... EXPECTED VALUE: A company has produced a new line of sweetener that it plans to market. They estimate ... BINOMIAL: Suppose that a website statistics shows that 30% of those who visit the website ... The mea

### Determining 95% Confidence Interval and Mean

Julie is an industrial psychologist. She is currently studying stress among executives of health corporations. She developed a survey that he believes measures stress. A score of 80 indicates dangerous stress. A random sample of 15 executives revealed the following stress scores. Score 94 78 83 90 78 99 97 90 97 98

### Manually Calulating Confidence Interval for Population Mean

Provide further clarification for this problems. I was given the answers, but having problem showing how to get the answer manually. Not to use Excel, but learning how to get to the answer manually. If X(bar) = 50, S=15, and n= 16, and assuming that the population is normally distributed, construct a 99% confidence interval e

### Confidence Interval Quality Control Managers

The quality control manager at a light bulb factory needs to estimate the mean life of a large shipment of light bulbs. The standard deviation is 100 hours. A random sample of 64 light bulbs indicated a sample mean life of 350 hours. A. Construct a 95% confidence interval estimate of population mean life of light bulbs in thi

### Descriptive Statistics, Probability & Confidence Interval

1. Calculate the mean, median and standard deviation of the following data: 10, 16, 12, 20, 18, 209, 16, 11, 13, 14, 17, 20, 25 2. Prepare a relative frequency histogram of the following data, use 4 classes. 43, 35, 41, 41, 39, 38, 41, 40, 45, 43, 52, 36, 43, 38, 39, 44, 45, 30, 37, 40, 39, 41, 44, 46, 39, 40, 44, 37, 4

### Statistics: proportion of customers who have a VISA card with the bank.

The First National Bank of Wilson has 650 checking account customers. A recent sample of 50 of these customers showed 26 to have a VISA card with the Bank. Construct the 99 percent confidence interval for the proportion of checking account customers who have a VISA card with the bank.

### Construct a 99 Percent Confidence Interval for Customers

The First National Bank of Wilson has 650 checking accounts customers. A recent sample of 50 of these customers showed 26 to have a VISA card with the Bank. Construct the 99 percent confidence interval for the proportion of checking account customers who have a VISA card with the bank.

### Confidence intervals of grade point averages

General Motors pays for employee education. The HR director would like to conduct a study on the average GPA of employees who have used this benefit to complete their degrees using a sample of education records over the past 10 years. GPA's range between 2.0 and 4.0. The mean GPA is estimated to be plus or minus .05 the populati

### 95% confidence interval

What would be the 95% confidence interval for this difference? 95% CI = mean difference +/- 2(standard error of the difference) t = 5.185 df = 13201 mean dif = -.16 Std. Error Dif = .031 95% CI (lower -.221) (upper -.100)

### Confidence Interval for the Mean Difference

A. In a random sample of 500 people aged 20-24, 22% were smokers. In a random sample of 450 people aged 25-29, 14% were smokers. Construct a 95% confidence interval for the difference between the population proportions. You may assume the samples are independent. You will be asked to identify each of the following. 1. Th

### Confidence Interval

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. Is it reasonable that the population mean is 28 weeks?

### Random sample

1. The mean replacement time for a random sample of 12 microwave ovens is 8.6 years with a standard deviation of 4.2 years. Construct a 98% confidence interval for the population variance o^2. Assume the data are normally distributed. A. (7.8,63.6) B. (1.9,15.1) C. (2.8,8.0) d. (7.4,54.3) 2. The dean of a major university

### Confidence Interval for Conusmer Purchase Amounts

Purchase Amounts for all Customers Shopping at a Local Supermarket on a Given Friday 4. Data of the amount that customers spend in a supermarket on a specific Friday. Assume this data represents the population. (20 points) a. What sample size would be required to be 95% sure that the estimate is within + \$10? b. How woul

### Hypothesis testing and conclusions

1. A machine produces 3-inch nails. A sample of 10 nails was selected and the lengths determined. The results are as follows: 2.89 2.95 3.00 3.05 2.99 2.96 3.10 3.06 3.00 3.12 Use these results to test H0: &#61549; = 3 and Ha: &#61549; &#61625; 3 at &#61537; = 0.01. Give the criti

### Confidence Interval for Population Mean: Weight of Trucks

A highway inspector needs an estimate of the mean weight of trucks crossing a bridge on the Interstate highway system. She selects a random sample of 49 trucks and finds a mean of 15.8 tons. The population standard deviation is known to be 3.85 tons. What is the 90 percent confidence interval for the population mean?

### Solving a Margin of Error Problem

The director of admissions has had questions from potential freshmen regarding the average price of textbooks per semester. In order to make an informed estimate of this cost, he selected a sample of 100 students and recorded their text book expenses for the most recent semester. He found a sample mean of \$391.52. He assumes th