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Confidence Interval

Sample size for estimating a population mean

An estimate is needed of the mean acreage of farms in Manitoba, Canada. The estimate should be correct to within 100 acres with probability 0.95. A preliminary study suggests that 500 acres is a reasonable guess for the standard deviation of farm size. How large a sample of farms is required and given that random sample size

Confidence Interval

Dave the jogger runs the same route every day (about 2.2 miles). On 18 consecutive days, he recorded the number of steps using a pedometer. The results were 3450 3363 3228 3360 3304 3407 3324 3365 3290 3289 3346 3252 3237 3210 3140 3220 3103 3129 Construct a 90 percent confidence interval for the true me

Confidence interval estimation for regression coefficients

1 What is the R^2 Value for your regression equation? 2 What is the value of the coefficient of Blue Collar in your equation? 3 What is the lower limit of the 95% CI for this coefficient? 4 What is the upper limit of the 95% CI for this coefficient?

Statistics

A supervisor for a large company wishes to estimate the proportion of parts from a supplier that are defective. He has selected a random sample of n = 200 incoming parts and has found 11 to be defective. Based on a 95% confidence level, the upper and lower limits for the confidence interval estimate are approximately 0.0234 to 0

Confidence interval and Hypothesis testing problems

Question 1: Confidence Interval for Effects of Marijuana Use on College Students: Data: Items sorted correctly by light marijuana users: n = 64, x = 53.3, s = 3.6 Items sorted correctly by heavy marijuana users: n = 65, x = 51.3, s = 4.5 Q: Refer to the sample data above and construct a 98% confidence interval fo

Confidence Interval for the True Mean

8.48 A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below: 0 26

Confidence Intervals and Mean Chloride Level

A laboratory in Florida is interested in finding the mean chloride level for a healthy resident in the state. A random sample of 70 healthy residents has a mean chloride level of 102 mEg/L. If it is known that the chloride levels in healthy individuals residing in Florida have a standard deviation of 35 mEg/L find a 90% confiden

Confidence Intervals - House Prices

Please solve attached. Suppose that a random sample of fourteen recently sold houses in a certain city has a mean sales price of $280,000, with a standard deviation of $9000. Under the assumption that house prices are normally distributed, find a 90% confidence interval for the mean sales price of all houses in this community

Statistics - Solving Confidence Intervals Problems

In a sample of 200 college seniors, 168 responded positively when asked if they have spring fever. Based on this, compute a 90% confidence interval for the propotion of all college seniors who have spring fever.

Confidence interval estimation .

The security department of a state university is planning its budget for the next year. In estimating the man-hours for security during university sponsored music concerts, the average length of music concerts is needed. A random sample from thirty-six security departments at universities was taken and the sample mean length o

Benefits of Confidence Intervals

Please help with the following problem. Describe a business situation that you have had or might face that will benefit from the use of confidence intervals?

Hypothesis testing and confidence intervals

Assume that in a hypothesis test with null hypothesis H 0: mu = 14.0 at alpha = 0.05, that a value of 13.0 for the sample mean results in the null hypothesis being rejected. That corresponds to a confidence interval result of: a) the 95% confidence interval for the mean contains the value 14.0 b) the 95% confidence interval

Salary Difference Between Degrees and Experience

We will be comparing the different salary ranges between those who have a Bachelor's Degree and those who have 10 years of experience. A random sample of 15 salaries that have a mean of $36,232. If the population standard deviation of those who have a Bachelor Degree or 10 years experience is $14,796.55, then what is the likelih

Sampling distribution of MEANS!

Let's say there is a local company (rhymes with "Zaplan") that promises a score of 625-good enough for admission to your favorite graduate school-if you take their $1200 preparatory course. 1. Treat yourself as a sample of 1 (N=1). Is a score of 625 significantly higher than average? Is it worth $800? Explain how you use a

Probability and confidence interval problems

A. Margaret Morris just correctly computed a standard deviation of 6.0 from a sample of 50 observations. What is the variance of Margaret's sample? b. Kim Fernando has just found the variance of a sample of 32 observations to be 64.0 by using a formula that is programmed into her new calculator. Therefore, what is the samp

Statistic Concepts: Estimates and Confidence

Part A: Define (a) point estimate, (b) interval estimate, (c) confidence interval, and (d) confidence level. Part B: List some common confidence levels. Why not use other confidence levels? Explain.

Confidence interval

A lightbulb manufacturer wants to estimate the total number of defective bulbs contained in all of the boxes shipped by the company during the past week. Production personnel at this company have recorded the number of defective bulbs found in each of 50 randomly selected boxes shipped during the p

Defective Lightbulbs in a Given Shipments

A lightbulb manufacturer wants to estimate the total number of defective bulbs contained in all of the boxes shipped by the company during the past week. Production personnel at this company have recorded the number of defective bulbs found in each of 50 randomly selected boxes shipped during the past week. There data are provid

Confidence interval estimation problems

Please help with the following problem. Car Antifreeze: A container of car antifreeze is supposed to hold 3785mL of the liquid. Realizing that fluctuations are inevitable, the quality-control manager wants to be quite sure that the standard deviation is less than 30mL. Otherwise, some containers would overflow while other

Confidence interval for a proportion: Example problem

Death Penalty Survey: In a Gallup poll, 491 randomly selected adults were asked whether they are in favor of the death penalty for a person convicted or murder, and 65% of them said that they were in favor. a. Find the point estimate of the percentage of adults who are in favor of this death penalty. b. Find a 95% confidence

Confidence interval for the population mean

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, deve

Calculating Confidence Interval Estimate for True Mean

A snack food manufacturer selected a sample of 15 bags of pretzels off the assembly line and weighed their contents. If the sample mean is 10.0 and the sample standard deviation is 0.15, find the 95% confidence interval estimate for the true mean weight of bags of this type of pretzel. A.(9.92, 12.34) B.(8.54, 11.46) C.(10

Confidence Intervals and Limits for a Proportion Question

A survey of 85 families showed that 36 owned at least one DVD player. Find the 99% confidence interval estimate of the true proportion of families who own at least on DVD player. Place your limits, rounded to 3 decimal places, in the blanks. Simply provide the numerical values and decimal point if appicable. For example, 0.1

Confidence Interval Estimate for the population mean

A lawyer researched the average number of years served by 45 different justices on the Supreme Court. The average number of years served was 13.8 years with a standard deviation of 7.3 years. What is the 95% confidence interval estimate for the average number of years served by all Supreme Court justices? Rround to 1 decimal

Construction of 95 Percent Confidence Intervals

8.18 In a sample of 500 new Web sites registered on the Internet, 24 were anonymous (i.e., they shielded their name and contact information). (a) Construct a 95 percent confidence interval for the proportion of all new Web sites that were anonymous. 8.21 A 2003 survey showed that 4.6 percent of the 250 Americans surveyed

Confidence Interval Estimate

When estimating a population mean with a confidence interval estimate, then E is: A) equal to the level of confidence. B) one-half the width of the confidence interval. C) a multiple of the population mean. D) a multiple of the population standard deviation.

Statistics - Confidence Interval Calculation

The lifetime of a certain brand of battery is known to have a standard deviation of 16 hours. Suppose that a random sample of 70 such batteries has a mean lifetime of 41 hours. Based on this sample, find a 90% confidence interval for the true mean lifetime of all batteries of this brand. Then complete the table below. Carry

Confidence Intervals: Upper and Lower Limit

A sociologist is studying the prevalence of crime in one major city. In a sample of 225 randomly selected residents, 60 say that they have been victimized by a criminal. Based on this sample, construct a 95% confidence interval for the proportion of all residents in this city who have been victimized by a criminal. Then complete

Making Interferences from Data

Assume a 95% confidence interval for u-turns out to be (1,000 2,000). To make more useful inferences from the data, the researcher wants to reduce the width of the confidence interval. Which of the following will result in a reduced confidence interval width?