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# Confidence Interval

### Confidence Interval for mean

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. Need the following answered, please see attached worksheet: 1) Construct a 95 percent confidence interval for the po

### 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

### Confidence interval estimation

The data that you will be using for this exercise came from a survey of two insurance carriers. The first carrier (C1) was compared against the second competitor (C2). The insurance company management team wants to know how Carrier 1 compared to the second carrier. Data from 159 respondents are included. All of the 5

### 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

### Histograms and Confidence Intervals for Surveys

The data that you will be using for this exercise came from a survey of two insurance carriers. The first carrier (C1) was compared against the second competitor (C2). The insurance company management team wants to know how Carrier 1 compared to the second carrier. Data from 159 respondents are included.

### 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

### Statistics problem

Problem 24 A real estate agent has collected a random sample of 75 houses that were recently sold in a suburban community. She is particularly interested in comparing the appraised value and recent selling price of the houses in this particular market. The value of these two variables

### 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

### What is the lower limit of the confidence interval? What is the upper limit of the confidence interval

Confidence interval for the population mean: Use of the t distribution A certain brokerage house wants to estimate the mean daily return on a certain stock. A random sample of 10 days yields the following return percentages: 2.46 2.54, -2.08, 0.72, 0.54, -0.47, -0.62, -2.01, -2.48, 2.36 If we assume that the returns

### 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?

### Find a confidence interval for a population proportion.

In response to media inquiries and concerns expressed by groups opposed to violence, the president of a university with over 25,000 students has agreed to survey a simple random sample of her students to find out whether the student body thinks the school's "Plundering Pirate" mascot should be changed to one that is less aggress

### 95% confidence interval of average torque

An assembly process includes a torque wrench device that automatically tightens compressor housing bolts; the device has a known process standard deviation of o=3lb-ft in the torque applied. a simple random sample of 35 nuts is selected, and the average torque to which they have been tightened is 150 lb-ft. What is the 95% confi

### Confidence interval estimation ..

A stationery store wants to estimate the total retail value of the 300 greeting cards that it has in its inventory. What are the upper and lower limits of the 95% confidence interval estimate of the population total value of all greeting cards that are inventory if a random sample of 20 greeting card indicates an average value o

### Confidence intervals of employees failing drug tests

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