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Confidence Interval

Confidence interval for mean

3. in an effort to estimate the annual income for new graduates, data were collected from 500 new graduates over a one -year period. assume a population standard deviation of $500. a) if the sample mean is $15,000, what is the 95% confidence interval for the population mean? b) if the sample mean is $15,000, what is the 98

Confidence

9.4 An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm. 9.6 The heights of a

From the Data Set below select a sample of 20 values and find the 90% confidence interval of the mean of the number of the acres. Find the mean of all values, and determine if the confidence interval contains the mean.

Problem: From the Data Set below select a sample of 20 values and find the 90% confidence interval of the mean of the number of the acres. Find the mean of all values, and determine if the confidence interval contains the mean. DATA SET VI Acreage of U.S. National Parks, in Thousands of Acres 41 66 233 775 1

Confidence interval

In an effort to estimate the mean amount spent per household per month in a small Canadian town, data were collected for a sample of 50 households. The sample showed an average amount of $2000 and a standard deviation of $500. a. Develop a 90% confidence interval estimate of the population mean amount spent. b. D

Sampling Variability and Standard Error

Based on a simple random sample of one hundred an analyst estimates the average hourly wage earned by workers in a city to be $30 and computes the margin of error to be $5. Can we conclude from this that most workers there earn between $25 and $35 per hour? Is this the right interpretation for the margin of error?

Variance of Repair Cost for Dishwashers

1.) The following data set represents the repair cost (in dollars) for a random sample of 30 dishwashers (adapted from Consumer Reports) 41.82 90.07 100.05 118.77 52.81 90.35 101.32 119.01 57.80 91.68 103.59 120.70 68.16 91.72 104.19 140.52 73.48 93.01 105.62 141.84 78.88 95.21 111.32 147.06 88.13

Confidence interval for population mean problem

Ford Motor Company wishes to estimate the mean dollar amount of damage done to a 1995 Taurus as result of a 10 mph crash into the rear bumper of a parked car. 36 Tauruses are test crashed into parked cars and the dollar amount of damage done to each is recorded. The results are x-bar = $438 and s=$86. a. Compute the 90% confi

Width of the confidence interval

Discuss what happens to the width of the confidence interval as the sample size is decreased. Discuss what happens to the width of the confidence interval as the confidence level is increased. Is this reasonable? Explain.

Confidence Interval and Sample Size Determination

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

Forecasting

Forecasting is not to clear to me, how do I get started? Given the following data on hotel check-ins for a 6-month period: Month Number of rooms July 70 August 105 September 90 October 120 November 110 December 115 a. What is the 3-month moving average for January? b. What is the 5-month moving average for Jan

A) Determine the 95% confidence interval estimates of the mean medical costs for each of the four age categories. b) For each year listed, determine the 95% confidence interval estimates of the total medical costs for Canadians 45 years old and older.

12.3-question 1 A statistics practitioner has been given the task of making these predictions. Accordingly, random samples of four groups of Canadians were drawn. They are Group Ages 1 45-64 2 65-74 3 75-84 4 85 and over Age group 2011 2016 2021 2026 2031 45-64 9718 10013

Speculations about a study result

This question is asking for speculation about the possible results of a study if we change the size of the population. It all depends on unknowns such as how representative the 100 adults are of the population. In general, the larger the population the more sure we are that it is representative of the population. In a poll o

99 percent confidence interval

1. A sample set of weights in pounds are 1.01, .95, 1.03, 1.04, .97, .97, .99, 1.01 and 1.03. Assume the population of weights are normally distributed. Find a 99 percent confidence interval for the mean population weight. 2. Based on a random sample of 25 units of product X, the average weight is 102 lbs. and the sample

95 percent confidence interval

Of a random sample of 600 trucks at a bridge, 114 had bad signal lights. Construct a 95 percent confidence interval for the percentage of trucks that had bad signal lights.

Determining a confidence interval

Computer Services, Inc., wants to determine a confidence interval for the average CPU time of their teleprocessing transactions. A sample of 64 transactions yielded a mean of 6 seconds with a standard deviation of 0.8 seconds. Determine a 98% confidence interval for the average CPU time.

Confidence interval for mean

2. A physician wanted to estimate the mean length of time μ that a patient wanted to see him after arriving. A random sample of 64 patients showed a mean waiting time of 23.4 minutes and a standard deviation of 7.1 minutes. Find a 95% confidence interval for μ.

Confidence Interval

A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what size sample should be taken so that at 95% confidence the margin of error will be 2 months or less?"

Confidence Interval for Time Spent on Computer Terminals

In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one week period. Assume the population standard deviation is 1.8 hours. If the sample mean is 9 hours, then the 95% confidence interval is?

Hypothesis Testing and Confidence Interval Problems

1. Two teachers give the same standardized statistics test. The results are: Teacher 1 Mean=75 N=20 Teacher 2 Mean=80 N=15 a. What would be a 95% confidence interval for each of the classes? b. The true mean for the test is 70, with a standard deviation of 5. Can you draw any conclusions about either of the clas

Confidence interval and Normal distributions

In a class there are 60 students. The mean exam score is 70 and the standard deviation is 5. (Be Precise in your answers!) Assume symmetric distribution of the scores. (i) What can you say about the number of students that have scores between 55 and 85? (ii) What can you say about the number of students who ha

Estimation:

The management of a department store is interested in estimating the difference between the mean credit purchases of customers using the store's credit card versus those customers using a national major credit card. You are given the following information. Store's Card Major Credit Card Sample size 64 49 Sample mean $140 $1

CONFIDENCE INTERVAL

The 95 percent confidence interval states that 95 percent of the sample means of a specified sample size selected from a population will lie within plus and minus 2.58 standard deviations of the hypothesized population mean. TRUE/FALSE

Confidence interval for mean methods

The association of coffee growers in Puerto Rico wants to know the average pounds of coffee consumption per week in towns in the metropolitan area. In a study conducted recently by the average of 81 persons was 1.5 pounds a week and a standard deviation of 0 .10. 1) What is the value of the average population? 2) What distri

Frequcny distribution chart and confidence interval

Scenario: You are an associate assigned to the claims department of a major insurance company. A policy holder has had an accident with his classic 1968 Oldsmobile Cutlass Supreme. At issue is the consideration of his brakes. Recently, he was driving down the road and was apparently unable to stop in time when a woman driv

Confidence interval for the ratio of population variances

Confidence interval for the ratio of population variances Actuaries use various parameters when evaluating the cost of a life insurance policy. The variance of the life spans of a population is one of the parameters used for the evaluation. Each year, the actuaries at a particular insurance company randomly sample 25 people wh

Hypothesis and confidence intervals

(1) A sample of 49 observations is taken from a normal population with a standard deviation of 10. The sample mean is 55. Determine the 99 percent confidence interval for the population mean. (5) A research firm conducted a survey to determine the mean amount steady smokers spend on cigarettes during a week. They found the di