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Confidence Interval

Statistics Problems

1. Given a normal distribution with mean,m =100 and standard deviation, s = 10, if you select a sample of n=25, what is the probability that x is a. less than 95? b. between 95 and 97.5? c. above 102.2? d. There is a 65% chance that X is above what value? 2. Time spent using e-mail per session is normally distri

Finding the confidence interval for poll or survey results

Quality Progress, Feburary 2005, reports on the results achieved by Bank of America in improving customer satisfaction and customer loyalty by listening to the "voice of the customer". A key measure of customer satisfaction is the response on a scale from 1 to 10 to the question: "Considering all the business you do with Bank of


1) The Target Corporation personnel director wants to estimate the number of employees within one year of retirement. A random sample of 120 employee records is selected, and 36 people are found to be within one year of retirement. Formulate an 84% interval estimate for the true proportion of employees within one year of retir

Statistics Problems: Mean, probability, standard deviation, confidence interval

1. You are a manager of a Starbucks located at Southcenter Mall. Recently, a new local coffee shop specializing in lattes has opened in the Mall. You are wondering what the impact on your latte sales may be. You know from previous data tracking that the largest number of lattes sold at your location is during the morning. T

Bank customer and bank manager

In the bank customer waiting time case, a bank manager had developed a new system to reduce the time customers spend waiting to be served by tellers during peak business hours. Typical waiting times during peak business hours under the current ystem are roughly 9 to 10 minutes The bank manager hopes that the new system will lo

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-

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 l

Statistics: Hypothesis Test, Confidence Interval Approach

1. In 2001, the US Department of Labor reported the average hourly earnings for US 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 earnings

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

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

Salary of assembly line workers; time to build a house in Kamloops

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

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

Confidence Interval Estimate of standard deviation of amounts of lead in the air

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

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

Normal Probability, Samples and Confidence intervals

1- The EMT industry reports that the average time it takes to respond to an emergency call is 25 minutes. Assume that is time is normally distributed with a sigma of 4 minutes. What percentage of call will be responded to in less than 20 minutes? 2- To qualify for the Police Academy, a candidate must score the top 15% on the

10 Problems on Descriptive Statistics, Point Estimates and Confidence Interval

1. Use the confidence interval to find the estimated margin error. Then find the sample mean. A biologist reports a confidence interval of (1.8, 3.0) when estimating the mean height (in centimeters) of a sample of seedlings. The estimated margin of error is______. The sample mean is _________. 2. You work for a consume

Constructing confidence intervals

We will be constructing confidence intervals for the proportion of each color as well as the mean number of candies per bag. Use the methods of 6.3 for the proportions and 6.1 for the mean. If calculating by hand, be sure to keep at least 4-6 decimal places for the sample proportions to eliminate large rounding errors.

Statistics Problems

6.10 Margin of error and the confidence interval. A study based on a sample of size 25 reported a mean of 93 with a margin of error of 11 for 95% confidence. (a) Give the 95% confidence interval. (b) If you wanted 99% confidence for the same study, would your margin of error be greater than, equal to, or less than 11? Expl

Calculation of Confidence Interval and Sample Size

Please show work, step by step. 1) Suppose a fast food restaurant wishes to estimate average sales volume for a new menu item. The restaurant has analyzed the sales of the item at a similar outlet and observed the following results: X = 500 (mean daily sales) s = 100 (standard deviation of sample) n = 50 (sample size)