Explore BrainMass

# Confidence Interval

### Develop a 95% confidence interval estimate for the mean of the population

1. An printout of the descriptive measures of daily checking account balances (in \$) of bank customers is shown below. Develop a 95% confidence interval estimate for the mean of the population of the checking balances. Account Balance Information Mean 4828.29 Median 5115.25 Mode 4976.50 Standard Deviation 1143.57 Sampl

### Confidence Intervals in Professions

Dr Patton is a professor of English. Recently he counted the number of misspelled words in a group of student essay. For his class of 40 students, the mean number of misspelled words was 6.05 and the standard deviation 2.44 per essay. Construct a 95% confidence interval for the mean number of misspelled words in the population o

### z-score and 90% confidence interval

1. The average hourly wage of workers at a fast food restaurant is \$7.85 with a standard deviation of \$0.35. Find the z value for each of the following pay rates. a. \$8.00 b. \$7.50 2. A sample of 60 faculty members at a large university found that their average taxes were \$500 a month, with a sample standard deviation

### Statistics: Comparisons Involving Means and confidence interval

FedEx and United Parcel Service (UPS) are the world's two leading cargo carriers by volume and revenue. According to the Airports Council International, the Memphis International Airport (FedEx) and the Louisville International Airport (UPS) are two of the ten largest cargo airports in the world. The following random samples (in

### Values for Confidence Intervals

Find the z and t values for the follow confidence intervals. Note that sample size does not apply for a z value. Compare the z value for 95% with the two t values for 95%. All the confidence levels are the same. Comment on the z and t values; are they different? Why, do you think? See the attached file.

### Statistic Problem

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 us

### Confidence Intervals and Margin of Error

Need assistance setting up and solving this problem: The National Center for Education Statistics reported that 47% of college students work to pay for tuition and living expenses. Assume that a sample of 450 college students was used in the study. a. Provide a 95% confidence interval for the population proportion of colleg

### Number of Respondents Required

In a public opinion poll 48% of 189 respondents favor an elimination of taxes on dividend income. How many respondents would be needed to calculate a 95% confidence interval (for the proportion of people who favor an elimination of taxes on dividend income) that has a total width no greater than 4% (the estimate must be within +

### Statistics : Point Estimates and Confidence Intervals

Many stock market observers say that when the p/e ratio for stocks gets over 20 the market is overvalued. (the p/e ratio is stock price divided by the most recent 12 months of earnings.) Suppose you are interested in seeing whether the current market is overvalued and would also like to know the proportion of companies that pay

### Confidence intervals for rational-emotive and client-centered approaches

Group 1: rational-emotive approach scores: 56, 42, 38, 41, 42, 25, 66, 38, 55, 61 Group 2: client-centered approach scores: 51, 45, 43, 40, 48, 22, 61, 51, 64, 56 Calculate and interpret 90%, 95%, and 99% confidence intervals for both groups of approaches. Also provide 90%, 95%, and 99% confidence intervals for both groups

### Statistics - 95% error margin and 98% confidence interval

1. A company wishing to improve its customer service collected hold times from 75 randomly selected incoming calls to its hot line that were put on hold. These calls had sample mean hold time = 3.4 minutes and s = 2.3 minutes. Is the claim that &#956; > 3.0 minutes substantiated by these data? Test with &#945; = .05. 8.95

### Confidence interval 95%

The batteries used in a digital watch have a operating life that is normally distributed. A sample of 16 batteries reveals a mean of 3.45 years and a standard deviation of 0.3 years. For 15 df, the area in the right tail of the t distribution is 0.10 if t = 1.341, 0.05 if t = 1.753, and 0.025 if t = 2.131. The width of a 95% co

### 95% confidence interval - statistics

Hack Wilson¿s major league record of 190 runs batted in during a single season in professional baseball has stood for 70 years. Perhaps the reason for this longevity is that the average for all the other league leaders is so far below the total Wilson knocked in back in 1930. A confidence interval might provide a clue. A random

### Applying statistics to a variety of situations

1. The time it takes for a taxi to drive from the office to the airport was recorded on 40 occasions. It was found that minutes and s = 5 minutes. Give (a) An estimate of ì = population mean time to drive. (b)An approximate 95.4% error margin. 2 On a Thursday, students were asked to report the number of hours sleep t

### Confidence Intervals

Calculate and interpret 90%, 95%, and 99% confidence intervals for both groups of approaches. Also provide 90%, 95%, and 99% confidence intervals for both groups when the sample size is increased from 10 to 50. Interpret all statistics Group 1: rational-emotive approach scores: 56, 42, 38, 41, 42, 25, 66, 38, 55, 61 Group

### Mean Score Confidence Interval for a Mental Health Questionnaire

A nursing professional conducts an analysis to examine scores on the mental health service and treatment outcome questionnaire. A sample of 16 patients gives the following summary statistics for one item addressing health problems: N Mean S 16 907.75 8.4814 Give a 95% confidence interval for the mean score.

### Sample Size for Criminology

A criminology professor has been teaching graduate and undergraduate statistics for a few years. Her records show that the overall mean for final exam scores is 82 with a standard deviation of 10. The professor believes that this year's class is superior to her previous classes. She decides to conduct a test on the 25 students

### Statistics Problem: Confidence Interval

A sample of 30 patients was studied in an effort to assess agency' preparedness for delivery of mental health services to African Americans. A nursing researcher and counselor decided to collaborate and conduct the study using the Clinical Attitudes, Knowledge, and Skills Inventory (CAKSI) to assess preparedness for delivery of

### Confidence Interval for population mean

The union for a particular industry has determined that the standard deviation of the daily wages of its workers is \$22. A random sample of 100 workers in this industry has a mean daily wage of \$117. Find a 95% confidence interval for the true mean daily wage of all union workers in the industry. Then complete the table below.

### Confidence interval for the population mean: Use of the t distribution

Could you provide the excel spreadsheet so that I can input #s and find the lower limit and upper limit of the confidence interval. A sample question is: Suppose that a random sample of eleven recently sold houses in a certain city has mean sales price of \$290,000, with a standard deviation of \$7,000. Under the assumption

### Confidence interval for the population mean: house prices

Suppose that a random sample of eleven recently sold houses in a certain city has mean sales price of \$290,000, with a standard deviation of \$7,000. Under the assumption that house prices are normally distributed, find a 95% confidence interval for the mean sales price of all houses in this community. Carry your intermediate c

### Confidence Interval for a Population Proportion of All Scores

From a large number of actuarial exam scores, a random sample of 275 scores is selected, and it is found that 195 of these 275 are passing scores. Based on this sample, find a 95% confidence interval for the proportion of all scores that are passing. Carry your intermediate computations to at least three decimal places. Round yo

### Confidence interval for proportion

A magazine is considering the launch of an online edition. The magazine plans to go ahead only if it's convinced that more than 25% of current readers would subscribe. The magazine contacts a simple random sample of 500 current subscribers, and 137 of those surveyed expressed interest in subscribing. What should the compa

### Sample Size/Confidence Interval

2. A cheese processing company wants to estimate the mean cholestrol content of all one-ounce servings of cheese. The estimate must be within 0.5 milligram of the population mean. a. Determine the minimum required sample size to construct a 95% confidence interval for the population mean. Assume the population standard deviat

### Confidence Intervals for Gas Grills

1. You are given the sample mean and the sample standard deviation. use this information to construct the 90% and 95% confidence intervals for the population mean. Which interval is wider? A random sample of 32 gas grills has a mean price of \$630.90 and a standard deviation of \$56.70. A random sample of 156 fields of durum

### Confidence interval for the population mean

The Greater Pittsburgh Area Chamber of Commerce wants to estimate the mean time workers who are employed in the downtown area spend getting to work. A sample of 15 workers revealed the following number of minutes traveled. 29, 38, 38, 33, 38, 21, 45, 34, 40, 37, 37, 42, 30, 29, 35 Develop a 98 percent confidence interval f

### Interval Population Study

A study of 2008 traffic fatalities found that 800 of the fatalities were alcohol related: A) Construct the 95% confidence interval for the population proportion. B) Construct the 99% confidence interval fro the population proportion. C) Which interval is wider and why is it wider?

### Confidence Interval of the Mean Solution

A quick study found that the average time it took a person to find a new job was 5.9 months. If a sample of 36 job seekers was surveyed, find the 95% confidence interval of the mean. Assume the standard deviation is .8 months, and how would you explain this to a layperson?

### Confidence Interval of Automobile Shop Managers

An automobile shop manager timed six employees and found the average time it took then to change a water pump was 18 minutes. The standard deviation of the sample was 3 minutes. Find the 99% confidence interval of the true mean, and how would you explain the interval to the average layperson

### How many boxes must the processor sample to be 95 percent confident that the sample mean does not differ from the population mean by more than 0.2 pounds?

A processor of carrots cuts the green top off each carrot, washes the carrots, and inserts six to a package. Twenty packages are inserted in a box for shipment. To test the weight of the boxes, a few were checked. The mean weight was 20.4 pounds, the standard deviation 0.5 pounds. How many boxes must the processor sample to be 9