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# Confidence Interval

### 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

### 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

### Statistics: Confidence Interval Problem

See the attached Q8 file for proper format. Only use the attached documents to assist with your solution and a scientific calculator. Please show all working out so I can understand how you have solved the question, and do not use Excel. Q8 A study was carried out by JT Co. Regarding the stopping distance of a 1300 kilogr

### Confidence intervals for employees who took work on vacation

In a recent survey, 161 of 493 employees responded that they typically took work with them on vacation and 95 responded that there are unwritten and unspoken expectations that they stay connected. a. Construct a 90% confidence interval estimate for the population proportion of employees who typically take work with them on va

### Confidence interval for the population mean total fat

The data shown below represents the total fat, in grams per serving, for a sample of 20 chicken sandwiches from fast-food chains. Complete parts (a) through (d). 5 4 6 6 19 17 24 27 20 33 18 28 25 17 29 27 35 26 38 63 a. Construct a 99% confidence interval for t

### Confidence Interval

Can you show how to do this in Excel if possible? Question: 1. A scientist wants to estimate the proportion of plants with berries growing in a particular region. They want to be within 6% of the true proportion when using a confidence interval of 99%. How many plants must be sampled if no preliminary estimate is avai

### Testing of Hypothesis and Confidence Interval of Population Mean

Temperature measurements are recorded at 40 randomly selected different locations for a particular city. A sample mean of 20 degrees Celsius is obtained with a standard deviation of 1.5 degrees.. There are no outliers in the sample measurements. Test the claim that the population mean is 21 degrees Celsius. Use a 0.05 significan

### Confidence Intervals for mean; t test; hypothesis test for proportion

Confidence intervals/One sample hypothesis tests Directions: For #1, calculate and interpret the confidence interval. Please show your manual calculation or the software output. Please show your work if you calculated manually on #1. If you used statistical software, please show the output. 1: Confidence Intervals for t

### Amazon.com claims that its textbook prices are cheaper than those offered by the local college bookstore. To test this claim, you randomly select 15 textbooks that are sold by both. Data File TEXTBOOK gives the prices for those 15 randomly selected textbooks at the local college bookstore and at Amazon.com.

6. Amazon.com claims that its textbook prices are cheaper than those offered by the local college bookstore. To test this claim, you randomly select 15 textbooks that are sold by both. Data File TEXTBOOK gives the prices for those 15 randomly selected textbooks at the local college bookstore and at Amazon.com. a. Construct

### Tests from confidence intervals

A confidence interval for the population mean tells us which values of mean are plausible (those inside the interval) and which values are not plausible (those outside the interval) at the chosen level of confidence. You can use this idea to carry out a test of any null hypothesis. Ho:mean =Mo starting with a confidence interva

### Margin of Error and Confidence Interval for a Poll

A recent poll (fictitious) reports that President Obama's "approval rating" is 52% and a statement says, "This poll has an error rate of 3%." The poll sampled 1300 people. (Note: The "3%" is the "margin of error." There is no computation of the confidence interval formula needed). This is an application of a confidence inter

### AluminiCorp: Test Random Sample and Confidence Interval

AluminiCorp is a major producer of aluminum cans that produces 40 billion aluminum cans every year. You work as a quality control officer for AluminiCorp, and are responsible for ensuring that the aluminum cans produced meet certain specifications. Each can is supposed to consist of precisely 15 grams of aluminum, and the market

### Confidence Interval: Mean load needed to pull apart pieces of Douglas fir

How heavy a load (pounds) is needed to pull apart pieces of Douglas fir 4 in long and 1.5 inches square? Here are the data from students doing a laboratory exercise: 33,190 31,300 32,320 26,520 23,040 30,460 24,050 33,650 31,860 28,730 33,020 33,280 30,930 32,700 30,170

### Confidence Interval Validity for the Study Time of Students

A class survey in a large class for first year college students asked, "About how many minutes do you study on a typical weeknight?" The mean response of the 269 students was x (bar over the x) = 137 minutes. Suppose that we know that the study time follows a normal distribution with standard deviation = 65 minutes in the popula

### Statistics: Sample variability, and Introduction to statistical inferences

1. Consider a normal population with µ = 25 and &#963; = 8.0. (A) Calculate the standard score for a value x of 27. (B) Calculate the standard score for a randomly selected sample of 30 with = 27. (C) Explain why the standard scores of 27 are different between A and B above 2. Assume that the mean score on

### A mayoral election probability

A mayoral election race is tightly contested. In a random sample of 1,100 likely voters, 572 said they were planning to vote for the current mayor. Based on this sample, what is your initial hunch? If you calculated the 95% confidence interval around the mayorâ??s current proportion of votes, would you claim with 95% confidence

### Calculate price/value for share; standard deviation of security; rental agreement choice

9.4 You own one share in a company called Invest Co. Inc. Examining the balance sheet, you have determined that the firm has \$100,000 cash, equipment worth \$900,000, and 100,000 shares outstanding. Calculate the price/value of each share in the firm, and explain how your wealth is affected if: A. The firm pays out dividen

### Statistics: 35 golfers' scores, price of pizza, weight of wrestlers, business majors

1. A study of 35 golfers showed that their average score on a particular course was 92. The standard deviation of the population is 5. A. Find the best point estimate of the mean. B. Find the 95% confidence interval of the mean score for all golfers. C. Find the 95% confidence interval of the mean score if a sample of 60 golf

### Random Sampling in EXCEL and Confidence Interval Estimate

The employee benefits manager of a small private university would like to estimate the proportion of full-time employees who prefer adopting the first (i.e., plan A) of three available health care plans in the coming annual enrollment period. A reliable frame of the university's employees and their tentative preferences are in t

### Fact Finding trips by Congress: average cost, distribution, deviation, confidence interval

8-76. According to an investigative reporter (Jim Drinkard - Legislators want to Ground 'Fact-finding' Trips, USA Today, January 2006), members of Congress are coming under scrutiny for 'fact-finding' trips. Since 2000, members of Congress have made 6,666 trips paid for by private interests. The trips were worth about \$19.6 mill