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# Confidence Interval

### Applying statistics to a variety of situations

1. The time it takes for a taxi to drive from the office to the airport was recorded on 40 occasions. It was found that minutes and s = 5 minutes. Give (a) An estimate of ì = population mean time to drive. (b)An approximate 95.4% error margin. 2 On a Thursday, students were asked to report the number of hours sleep t

### Sample Size for Criminology

A criminology professor has been teaching graduate and undergraduate statistics for a few years. Her records show that the overall mean for final exam scores is 82 with a standard deviation of 10. The professor believes that this year's class is superior to her previous classes. She decides to conduct a test on the 25 students

### Statistics Problem: Confidence Interval

A sample of 30 patients was studied in an effort to assess agency' preparedness for delivery of mental health services to African Americans. A nursing researcher and counselor decided to collaborate and conduct the study using the Clinical Attitudes, Knowledge, and Skills Inventory (CAKSI) to assess preparedness for delivery of

### Confidence interval for the population mean: Use of the t distribution

Could you provide the excel spreadsheet so that I can input #s and find the lower limit and upper limit of the confidence interval. A sample question is: Suppose that a random sample of eleven recently sold houses in a certain city has mean sales price of \$290,000, with a standard deviation of \$7,000. Under the assumption

### What is the mean yearly sugar consumption for the American Sugar Producers Association?

The American Sugar Producers Association wants to estimate the mean yearly sugar consumption. A sample of 16 people reveals the mean yearly consumption to be 60 pounds with a standard deviation of 20 pounds. 1. What is the value of the population mean? What is the best estimate of this value? 2. Explain why we need to use t

### Hypothesis Testting, Confidence Intervals and Levels of Significance

In a statistics lecture, students are asked whether or not they enjoyed doing statistics. Random sample of 50 students was taken and 30 of them said that they enjoyed doing statistics. The lecturer claimed that more than 50% of the students enjoyed doing statistics. (i) Test, at the 5% level of significance, whether or not

### Confidence Intervals and Standard Deviation

In a manufacturing process, the diameter of the steel rods is the product characteristic. A random sample of 25 steel rods is taken and sample mean is 8.88 cm. The diameter is assumed to be normally distributed with standard deviation 1.25. (i) Find a 95% confidence interval for the true diameter. If the standard deviation

### Confidence Interval

A random sample of 172 students was asked to rate on a scale to from 1 (not important) to 5 (extremely important) health benefits as a job characteristic (note that the rating scale can also have decimals, i.e. a student can give a rating of 1.32). The sample mean rating was 3.31, and the sample standard deviation was 0.70.

### Confidence Interval

What is meant by confidence interval? Please explain with real life examples.

### Statistics - Confidence interval for mean and proportion

1. Find the critical value za/2 which corresponds to a degree of confidence of 98%. 2. Express the confidence interval in the form of p-hat plus or minus E. -0.052 < p < 0.568 3. Find the margin of error for the 95% confidence interval used to estimate the population proportion if n = 175 and x = 95. 4. Find the mini

### Mean/Standard Deviation

See attached file for full problem description. 1. The Internal Revenue Service is studying contributions to charity. A random sample of 36 returns is selected. The mean contribution is \$150 and the standard deviation of the sample is \$20. Construct a 98 percent confidence interval for the population mean. 2. A manufactu

### Confidence interval for mean and proportion

11. As part of a safety check, the Pennsylvania Highway Patrol randomly stopped 65 cars and checked their tire pressure. The sample mean was 32 pounds per square inch with a sample standard deviation of 2 pounds per square inch. Develop a 98 percent confidence interval for the population mean. 12. A survey of 4,000 colleg

### Estimates and sample size, estimating population variance

1. In considering the production of a new car accessory, the Michigan Manufacturer Company wants to do a marketing study to determine the proportion of cars with cellular phones. How many cars must be sampled to have 92% confidence that the sample proportion is in error by no more than 0.03? The answer is 851 need help setting

### Statistics Equations

1. Explain how the purpose of estimation differs from the purpose of a hypothesis test. 2. Explain why it would not be reasonable to use estimation after a hypothesis test for which the decision was "fail to reject Ho." 3. Explain how each of the following factors affects the width of a confidence interval: a. Increasing

### Population mean, sample size, sample mean

1. An upper-level sociology class at a large urban university has 120 students, including 34 seniors, 57 juniors, 22 sophomores and 7 freshmen. a). Imagine that you choose one random student from the classroom (perhaps by using a random number table). What is the probability that the student will be junior? b). What is the pro

### A college finds that the data on an achievement test for entering freshmen is mound-shaped and has a mean score of 60

1. A college finds that the data on an achievement test for entering freshmen is mound-shaped and has a mean score of 60 with a standard deviation of 6. If it admits any student who scores 54 or above, approximately what percent of the applicants will be refused admission? A. 34% B. 16% C. 84% D. 68% 2. The mean ti

### Confidence interval for mean of cycle time

Cycle Time 67.696 56.684 64.118 53.158 66.609 Question 66.623 47.507 What is the confidence interval for the Cycle Time? 76.022 67.497 38.815 59.449 49.47 51.259 55.991 44.522 89.973 66.651 54.697 77.258 18.505 58.354 24.056 50.781 84.328 70.17 66.169 48.589 65.022 40.90

### Information about "Confidence Interval for proportion"

From a large number of actuarial exam scores, a random sample of 375 scores is selected, and it is found that 270 of these 375 are passing scores. Based on this sample, find a 99% confidence interval for the proportion of all scores that are passing. Then complete the table below. Carry your intermediate computations to at le

### Confidence Interval for the Mean

Call Center 1 Call Center 2 19.14 20.64 24.59 27.42 28.37 25.68 27.17 20.45 29.52 18.55 18.97 23.91 24.53 22.84 29.33 22.33 18.42

### Confidence interval for true average degree of polymerization

Question: An article contained the following observations on degree of polymerization for paper specimens for which viscosity times concentration fell in a certain middle range. Degree: 429 421 421 422 425 427 431 436 437 439 446 447 448 452 453 463 465 a) Calculate a two-sided 98% confidence interval for

### Upper and Lower Confidence Limits

A journal article reports that a sample of size 5 was used as a basis for calculating a 95% confidence interval for the true average natural frequency (Hz) of delaminated beams of a certain type. The resulting interval was [216.3, 217.8] You decide that a confidence level of 99% is more appropriate than the 95% level used. Hint

### Confidence Interval Questions

A confidence interval is desired for the true average stray-load loss (watts) for a certain type of induction motor when the line current is held at 10 amps for a speed of 1500 rpm. Assume that stray-load loss normally distributed with sigma = 2.3 Give answer to three decimal places. Compute a 95% confidence interval f

### Confidence interval for population proportion

1. Consider the following results for independent samples taken from two populations. Sample 1 Sample 2 N = 400 n = 300 ¹ ² _ _ P = .48 p = .36 ¹ ² a. What is the p

### Confidence Interval for difference in means

A random sample of 40 men drank an average of 20 cups of coffee per week during finals, while a sample of 30 women drank an average of 15 cups of coffee per week. The sample standard deviations were 6 cups for the men and 3 cups for the women. The standard error for the difference between the two sample means is 1.095. Calcul

### Confidence interval for mean of breaking strength

Consider the trash bag problem. Suppose that an independent laboratory has tested trash bags and has found that no 30-gallon bags that are currently on the market have a mean breaking strength of 50 pounds or more. On the basis of these results, the producer of the new, improved trash bag feels sure that its 30-gallon bag will b

### Problems related to confidence interval, margin of error, z score and standard error of mean.

See attached file for full problem description. 1. A simple random sample of 40 items resulted in a sample mean of 25. The population standard deviation is = 5. a. What is the standard error of the mean, _ x ? b. At 95% confidence,

### Confidence Intervals and Significance Levels

68. In a study, Germination and Emergence of Broccoli, conducted by the Department of Horticulture at Virginia Polytechnic Institute and State University, a researcher found that at 5°C, 10 seeds out of 20 germinated, while at 15°C, 15 out of 20 seeds germinated. Compute a 95% confidence interval for the difference between t

### Confidence Interval: Breaking Strengths of Cables

The breaking strengths of cables produced by a certain manufacturer have a standard deviation of 82 pounds. A random sample of 150 newly manufactured cables has a mean breaking strength of 1950 pounds. Based on this sample, find a 95% confidence interval for the true mean breaking strength of all cables produced by this manufact

### Sample Size for Mean and Proportion Football Team

Part I. Suppose the coach of the football team wants to estimate the proportion of the population of fans who support his current starter lineup. The coach wants the estimate to be .04 of the true proportion. Assume a 99 percent level of confidence. The coach estimated the proportion supporting the current starter lineup to

### Confidence Intervals and Biased Estimators

6. The heights of a random sample of 50 college students showed a mean of 174.5 cm and standard deviation of 6.9 cm. a) Construct a 98% confidence interval for the mean height of all college students. b) What can we assert with 98% confidence about the possible size of our error if we e