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# Confidence Interval

### Confidence Intervals: New type of ammunition, measured velocity

Fifty rounds of a new type of ammunition was fired from a M-1, and the muzzle velocity of the projectile was measured. The sample had a mean velocity of 853 meters per second, with a standard deviation of 2.9 meters per second How do you know which Hypothesis Testing to use? A) Construct and interpret a 99% Confidence In

### Problems with Confidence interval for a population proportion

3.a) Consider the population of Wisconsin licensed drivers aged 20 or younger. A random sample of size 363 from this population is obtained. Fifty three (53) of these people state that they drink alcoholic beverages 'several times a week'. Find a 98% confidence interval for the proportion in the entire population who drink 'seve

### Margin of Error and Confidence Interval Assumptions

1. To estimate the average time it takes to assemble a certain computer component, the industrial engineer at an electronic firm timed 40 technicians in the performance of this task, getting a mean of 12.73 minutes and a standard deviation of 2.06 minutes. a. What can we say with 99 % confidence about the maximum error if x-

### Problem: Sample size for estimating a population mean

In a sample of 30 randomly selected women, it was found that their mean height was 63.4 inches. From previous studies, it is assumed that the standard deviation is 2.4. 1) Determine the minimum required sample size to construct a 99% C.I. for the population mean if estimate must be within .8 inch of the population mean.

### Sample size for estimating a population proportion.

In a survey of 262 smokers, 189 smokers considered themselves addicted to cigarettes. A) If you are wanting to estimate, with 98% confidence, the proportion of smokers who are addicted to cigarettes and your estimate must be accurate within 4% of the population proportion. Find the sample size needed using the study above.

### Large sample confidence interval for a population mean

A random sample of 56 fluorescent light bubs has a mean life of 645 hours with a standard deviation of 31 hours. A) Construct a 95% confidence interval for the population B) How would you increase the accuracy in this problem?

### Confidence Interval of Test Score Sample

See attached file for clarity. 1. The standard deviation of test scores on a certain achievement test is 10.7. A random sample of 60 scores on this test had a mean of 76.2. Based on this sample, find a 90% confidence interval for the true mean of all scores. Then answer: What is the lower limit of 90% confidence interval

### Confidence Interval of a Random Sample

In a random sample of 225 students at a university, 180 stated that they were nonsmokers. Based on this sample, compute a 95% confidence interval for the proportion of all students at the university who are nonsmokers. Carry your intermediate computations to at least three decimal places. Round your answers to two decimal pl

### Confidence Interval For Population Standard Deviation

Pilots who cannot maintain regular sleep hours due to their work schedule often suffer from insomnia. A recent study on sleeping patterns of pilots focused on quantifying deviations from regular sleep hours. A random sample of 20 commercial airline pilots was interviewed, and the pilots in the sample reported the time at which t

### Hypothesis Testing & Confidence Interval explained in this answer

A medical researcher estimates that no more than 55% of the U.S. adults eat breakfast every day. In a random sample of 250 U.S. adults, 56.4% say that they eat breakfast every day. At alpha =.01, is there evidence to reject the researcher's claim ? A) Test Statistic B) Graph C) Conclusion D) Construct a 99.9% C.I.

### Confidence Interval Estimate using t-Distribution

The level of various substances in the blood of kidney dialysis patients is of concern because kidney failure and dialysis can lead to nutritional problems. A researcher performed blood tests on several dialysis patients on 6 consecutive clinic visits. One variable measured was the level of phosphate in the blood. Phosphate leve

### Estimate of Population Mean

A random sample of 25 people employed by the Florida state authority established they earned an average wage (including benefits) of \$65 per hour. The sample standard deviation was \$6.25 per hour. (a) What is your best estimate of the population mean (b) Develop a 99 percent confidence interval for the population mean wa

### Statistics: Hypothesis Test, Confidence Interval Approach

1. In 2001, the U.S. Department of Labor reported the average hourly earnings for U.S. production workers to be \$14.32 per hour. A sample of 75 production workers during 2003 showed a sample mean of \$14.68 per hour. Assuming the population standard deviation is \$1.45, can we conclude that an increase occurred in mean hourly earn

### Statistics: hypothesis testing; sample size vs. margin of error

Basic concepts. For each of the following, answer the question and give a short explanation of your reasoning. (a) A 95% confidence interval for the difference between two means is reported as (- 0.1, 1.5). What can you conclude about the results of a significance test of the null hypothesis that the population means are equ

### mean number of gallons of gasoline sold to his customers

Bob Nale is the owner of Nale's Texaco GasTown. Bob would like to estimate the mean number of gallons of gasoline sold to his customers. Assume the number of gallons sold follows the normal distribution with a standard deviation of 2.6 gallons. From his records, he selects a random sample of 55 sales and finds the mean number of

### Statistics: Chapter 8, P23, P34' Chapter 9, P35, P33

Chapter 8 34. Information from the American Institute of Insurance indicates the mean amount of life insurance per household in the United States is \$110,000. This distribution follows the normal distribution with a standard deviation of \$40,000. a) If we select a random sample of 50 households what is the standard error of

### 7-12 confidence interval estimate of the population mean

7-12. Twelve different video games showing substance use were observed and the duration times of game play (in seconds) are listed below. The design of the study justifies the assumption that the sample can be treated as a simple random sample. Use the data to construct a 99% confidence interval estimate of (u), the mea durati

### The Margin of Error

Assume that a random sample is used to estimate a population proportion p. Find the margin of error E that corresponds to the given statistics and confidence level: 90% confidence; the sample size is 1600 of which 30% are successes The margin of error E= _____ (round to four decimal places as needed).

### What is the confidence interval for the population mean yearly premium for Families USA, a monthly magazine?

Families USA, a monthly magazine that discusses issues related to health and health costs, surveyed 18 of its subscribers. It found that the annual health insurance premiums for a family with coverage through an employer averaged \$10,450. The standard deviation of the sample was \$985. (a) Based on this sample information, de

### Normal, Samples Probabilities and Confidence Interval and Hypothesis Testing.

1- It has been reported that the mean income of parents of freshmen entering a particular university is \$91,600. The president of a neighboring university feels that the mean income of the parents of his university's freshman class have a mean income greter than \$91,600. The president selects 100 families randomly and finds the

### Probability, Confidence Interval

Please show all work. 1. Suppose the salary of assembly line workers has Normal distribution with mean of \$20,000, and standard deviation of \$3,000. a) What is the probability that a randomly selected assembly line worker earns more than \$22,000? b) What is the probability that the average salary of 5 assembly line

### Proportion of US citizens living where carbon monoxide levels are acceptable

1.) From a sample of 1201 U.S. citizens, it was discovered that 1139 lived in neighborhoods with acceptable levels of cabon monoxide. A) Obtain a point estimate for the proportion of U.S. citizens who live in neighborhoods with acceptable levels of carbon monoxide. B) Construct a 98% Confidence Interval for the proportio

### Confidence Interval for Mean: Math achievement scores

The math achievement scores for 15 female students who just finished high school in the U.S. are as follows.....433, 563, 418, 389, 411, 492, 520, 458, 442, 479, 398, 494, 454, 337, 514 a) Are the scores normally distributed? Explain? B) Mean = Variance = Standard Deviation = C) Construct a 95% C.I. for the mean achi

### Standard Error of Mean and Confidence Interval

1. Use the information given to calculate the standard error of the mean. Mean systolic blood pressure for a sample of n=324 men is =123.5, and the standard deviation is s=9. 2. If each of the following is decreased but everything else remains the same, will a confidence interval become wider, will it become narrower, or wil

### Statistics: probablitiles, confidence intervals, hyothesis testing for population of stocks

See attached data file. Using Excel, assume that the distribution of the population of all stocks on that index is normal, and using the mean and standard deviation from your sample as point estimates, find the following probabilities: P (a price is greater than \$20) P (a price is less than \$90) P (a price is between \$30

### Anxiety score for today's children; Doctor visits of dog owners

10. Standardized measures seem to indicate that the average level of anxiety has increased gradually over the past 50 years. In the 1950s, the average score on the child manifest anxiety scale was µ=15.1. A sample of n=16 of today's children produces a mean score of M=23.3 with SS=240. a. based on the sample, make a point es

### Motorola X Bar and confidence intervals

Motorola wishes to estimate the mean talk time for one of their new phones before the battery must be recharged. In a random sample of 35 phones, the sample mean talk time is 325 minutes. A) Why can we say that the sampling distribution of x-bar is appropriately normal? B) Construct a 98% Confidence Interval for the mean

### Confidence Interval Estimate of standard deviation of amounts

Listed below are (in micrograms per cubic meter, or mg/m3) in the air. An organization has established an air quality standard for lead of 1.5 mg/m3. The measurements shown below were recorded at a destroyed building on different days immediately following its destruction. Assume that this sample is a simple random sample obtai

### Confidence Interval Estimate of Standard Deviation

The body mass index (BMI) for a sample of men and a sample of women are given below. Assume the samples are simple random samples obtained from populations with normal distributions. [Please refer to the attachment for the data]. Construct an 80% confidence interval estimate of the standard deviation of BMIs for men.

### Statistics Problems

8. Assume that the salaries of elementary school teachers in the United States are normally distributed with a mean of \$34,000 and standard deviation of \$2000. What is the cutoff salary for teachers in the bottom 10%? 9. The lengths of pregnancies are normally distributed with a mean of 267 days and a standard deviation of 15