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# Confidence Interval

### Statistics: Memo to Universal Credit team about sample size

See the attached file. A partner company to American Intellectual Union (AIU), Universal Credit Inc., would like to examine the required sample size needed to be able to estimate the mean dollars that each card holder will spend each month. It would like to be within plus or minus \$55 of the true mean with a 95% confidence le

### 95% confidence level.

8.51 Suppose that a sample of 200 (stored in ItemErr) is selected from a population of 10,000 items. Of these, 10 items are found to have errors of the following amounts: 13.76 42.86 34.65 11.09 14.54 22.87 25.52 9.81

### Hypothesis test for proposed product of a notebook computer company

See attachment for format. 11.28 When companies are designing a new product, one of the steps typically taken is to see how potential buyers react to a picture or prototype of the proposed product. The product-development team for a notebook computer company has shown picture A to a large sample of pot

### Confidence Interval For Mean Price And Age Of Bank Employees

Please see attachment for data. 1. To find the confidence interval for the true mean of the "price in \$000" of all the employees in the bank, should the z-score or t-score be used?if so why? 2. Find a 95% and a 99% confidence level for "price in \$000" and "age" respectively using all the 80 data given that the population v

### Solve: Using the Confidence Interval for the Mean

In New York State, savings banks are permitted to sell a form of life insurance called the savings bank life insurance (SBLI). The approval process consists of underwriting, which includes a review of the application, a medical information bureau check, possible requisites for additional medical information and medical exams, a

### Confidence Interval for the Mean and Proportion

Scenario: A market researcher for a consumer electronics company wants to study the television viewing habits of residents of a particular area. A random sample of 40 respondents is selected, and each respondent is instructed to keep a detailed record of all television viewing in a particular week. The results are as follows:

### Statistics: Find the mean score and 95% confidence interval for student course scores

See attached file. Question 1. The data for question 1 is contained in the file, Course_Scores.xls. This problem concerns course scores (on a scale from 0-100) for a large undergraduate computer-programming course. The class is composed of both underclassmen (freshmen and sophomores) and upperclassmen (juniors and seniors)

### Audit: Find a 95% confidence interval for the total amount of receivables.

4-12 An auditor of a small business has sampled 50 of 700 accounts. The sample mean total receivables is \$453, and the standard deviation is \$86. Find a 95% confidence interval for the total amount of receivables.

### Statistics: Sampling error, estimated population mean, confidence interval

21. Ch 8. What is sampling error? Could the value of the sampling error be zero? If it were zero, what would this mean? 22. Ch 8. List the reasons for sampling. Give an example of each reason for sampling. 34. Ch 8. Information from the American Institute of Insurance indicates the mean amount of life insurance per hous

### Confidence Interval & Hypothesis Testing: Proportion

The topic of my project is to find out the number of patients that have used In Home Care as their home health agency for more than 2 years. In Home Care's goal is to have over 50% of their patients be with them over 2 years which would demonstrate the staff is providing adequate and satisfying healthcare to their patients. A s

### Normal Probability, Hypothesis Testing & Confidence Interval

See attached file for proper formatting. Please show work. From the book (Statistical Techniques in Business and Economics) By D. A. Lind/ W. G. Marchal/ S. A. Wathen. Chapter 8 1. Packages of sugar bags for Sweeter Sugar Inc. have an average weight of 16 ounces and a standard deviation of 0.24 ounces. The weights

### Confidence intervals for proportions of wrist injuries

A study of injuries to in line skaters used data from the National Electronic Injury Surveillance System, which collects data from a random sample of hospital emergency rooms. The researchers interviewed 161 people who came to emergency rooms with injuries from in line skating. Wrist injuries (mostly fractures) were the most c

### Confidence Interval for Mean and Proportion..

See attached file. Please show the formula and step used to solve these two problems. 3. A random sample of 10 parking meters in downtown Nashville showed the following incomes for a day. \$2.60, \$1.05, \$2.45, \$2.90, \$1.30, \$3.10, \$2.35, \$2.00, \$2.40, \$2.35 Find the 95% confidence interval of the true mean. 6. Out

### Inference about a population proportion: Times New Roman and Gigi preference

Plain type fonts such as Times New Roman are easier to read than fancy fonts such as Gigi. A group of 25 volunteer subjects read the same text in both fonts. (This is a matched pairs design. One sample procedures for proportions, like those for means, are used to analyze data from matched pair designs.) Of the 25 subjects, 1

### Sample Size & Margin of Error

An automobile manufacturer would like to know what proportion of its customers are not satisfied with the service provided by the local dealer. The customer relations department will survey a random sample of customers and compute a 99% confidence interval for the proportion who are not satisfied. (a) Past studies suggest t

### Population Proportion of students who took coaching courses

A random sample of students who took the SAT college entrance exam twice found that 427 of the respondants had paid for coaching courses and that the remaining 2733 had not. Give a 99% confidence interval for the proportion of coaching among students who retake the SAT. Use the following four step process: STATE: What is

### Confidence Interval Statistics for the Mean

1. Suppose you have drawn a simple random sample of 400 students from University X and recorded how much money each student spent on text books in Fall 2009. For your sample, sample mean (X-bar) is \$500, and sample standard deviation (s) is \$100. Construct a 99% confidence interval for the mean. 2. Suppose you have drawn a s

### Test the breaking strength of a sample of wood fibers

The breaking strength of a random sample of n = 20 bundles of wood fibers has a sample mean x-bar = 436.5 and sample standard deviation s = 11.90. Construct 90%, 95%, and 99% t-interval for the average breaking strength µ. Do you think that the average breaking strength is equal to 450.0? Please explain me why or why

### Statistics Two-Sample Problems: Durable Press cotton fabric; Permafresh method

"Durable Press" cotton fabrics are treated to improve their recovery from wrinkles after washing. Unfortunately, the treatment also reduces the strength of the fabric. A study compared the breaking strength of fabrics treated by two commercial durable press processes. Five swatches of the same fabric were assigned at random t

### Confidence Interval for Magnitudes

Given: X ̅ = 97, sx = 16, nx = 64, Y ̅ = 90, sY = 18, nY = 81; assume the samples are independent. Construct a confidence interval of μX - μY according to (a) C = .95 and (b) C = .99 Here are some notes: Rule for constructing a confidence interval for μX - μY when σx and σy are unknown (X ̅- Y ̅) ±t_p s_(

### Statistics: Business Week, CNBC survey, auto mileage tests, Eagle Outfitters hypothesis

Please see the files attached. Show all work. Please do first 4 problems. 1. Business Week surveyed MBA alumni 10 years after graduation (Business Week, September 22, 2003). One finding was that alumni spend an average of \$115.50 per week eating out socially. You have been asked to conduct a follow-up study by taking a s

### Graphs, Variables, Confidence Intervals, Population Mean Value, Highest EMV

See attachment for data. Q-1a. You run a small Internet business and are concerned about customer support service levels on the Help Desk. You want to know how many calls per day are handled by your help desk staff. You collect the data at left over a 90-day period. Use appropriate descriptive statistics to make sense of

### Statistics: 8 problems of Normal Probability, Samples, and CI

1-The average time it takes to complete a test is first-year statistics is 46.2 minutes. the standard deviation is 8 minutes. Assume the times for taking the test are normally distributed. a) What is the probability that a randomly selected individual completes the test is less than 43 minutes. b) For a randomly selected group o

### 95 % confidence interval and outlier removal example

Part 1: Using a previous exercise about Hallux abducto valgus (HAV) (deformation of the big toe that often requires surgery). Doctors used x-rays to measure the angle (in degrees) of deformity in 38 consecutive patients under the age 21 who came to a medical center for surgery to correct HAV. The angle is a measure of the ser

### Confidence interval for mean conductivity & stemplot

How well a material conducts heat matters when designating houses, for example. Conductivity is measured in terms of watts of heat power transmitted per square meter of surface per degree Celsius of temperature difference on the two sides of the material. In these units, glass has conductivity of about 1. The National Institu

### How to find the 95% confidence interval: BMI example

In a previous example about the body mass index of young women we developed a 95% confidence interval for the mean body mass index (BMI) of women aged 20 to 29 yrs, based on a national random sample of 654 such women. We assumed there that the population standard deviation was known to be 7.5. In fact, the sample data had mean

### Inference about a population mean: Confidence interval and stemplot

Our decisions depend on how the options are presented to us. Here's an experiment that illustrates this phenomenon. Tell 20 subjects that they have been given \$50 but can't keep it all. Then present them with a long series of choices between bets they can make with the \$50. Scattered among these choices in random order are 6

### Confidence Interval and Sample Size..

Could someone please share some knowledge on these questions. Needed to verify answers checking whether I do understand the concept thoroughly. File Attached with t-Distribution and Chi-Square Distribution charts. A Company surveys 32 randomly selected employees and ask the number spent working at home after hours during

### Confidence Intervals: Employee hours spent working at home

See Attachment. A company surveys 32 randomly selected employees and asks the number of hours spent working at home after hours during a week. The results are shown below: Using Excel, construct a 90% confidence interval for the mean hours worked.

### Confidence Interval for Population Proportion using Excel

Question: In a survey of 842 musicians, 715 said they began playing an instrument while in elementary school. Using Excel, construct a 90% confidence interval for the proportion of musicians who began playing an instrument while in elementary school.