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Confidence Interval

Department store chain, confidence interval for mean

1. A major department store chain is interested in estimating the average amount its credit card customers spent on their first visit to the chain's new store in the mall. Fifteen credit card accounts were randomly sampled and analyzed with the following results: Χ = $50.50 and s2 = 400. Assuming the distribution of th

To find the confidence interval of difference of mean

Construct a 90% confidence interval for mu sub d, the mean of the differences d for the population of paired data. Assume that the population of paired differences is normally distributed. d-bar = 3.125; s d = 2.911; n = 8 2.435 < <MUµd < 3.815 1.175 < µd < 5.075 2.435 < µd < 5.075

Calculating the Margin of Error

Use the confidence level and sample data to find the margin of error. Systolic blood pressure for women ages 18-24: 94% confidence; n = 81, x-bar = 113.8 mm Hg, sigma = 12.8 mm Hg Round to the nearest one decimal place. 2.7 mm Hg 2.6 mm Hg 42.6 mm Hg 9.0 mm Hg

Confidence interval and testing of hypothesis problems

1. A manufacturer of small appliances employs a market research firm to estimate retail sales of its products by gathering information from a sample of retail stores. This month an SRS of 75 stores in the Midwest sales region finds that these stores sold an average of 24 of the manufacturer's hand mixers, with standard deviatio

Confidence level - margin of error

Use the confidence level and sample data to find the margin of error E. Weights of eggs: 95% confidence; n = 49, x-bar = 1.70 oz, sigma = 0.33 oz

Confidence interval for a population mean

A researcher wishes to construct a 95% confidence interval for a population mean. She selects a simple random sample of size n=20 from the population. The population is normally distributed and sigma is unknown. When constructing the confidence interval, the researcher should use the t distribution; however, she incorrectly uses

Confidence level and sample data

Use the confidence level and sample data to find a confidence interval for estimating the population mean m. Test scores: n = 101, x-bar = 96.8, sigma = 8.3, 99 percent confidence

P-hat and Confidence Interval

The following confidence interval is obtained for a population proportion, p:(0.458, 0.490). Use these confidence interval limits to find the point estimate, p-hat.

Probability and Statistics

1. TFQ: Amy wants to find a 96% confidence interval for the amount of time it takes to get to work. She kept records for 35 days and found her average time to commute to work was 20.5 minutes with a standard deviation of 3.6 minutes. Amy's maximum error of estimate would be 1.25 minutes. 2. TFQ: Charles wants to be 90% c


Question 1: Find the number of successes x suggested by the given statement. Among 680 adults selected randomly from among the residents of one town, 27.2% said that they favor stronger gun-control laws. a. 183 b. 184 c. 186 d. 185 Solve the problem. In a game, you have a 1/29 probabilit

Construction of confidence interval for mean and population proportion.

* Construct the indicated confidence interval for the difference between population proportions p1 - p2. Assume that the samples are independent and that they have been randomly selected. x1 = 57, n1 = 95 and x2 = 84, n2 = 96; Construct a 98% confidence interval for the difference between population proportions p1 - p2. ....

Estimation: Confidence Intervals and Sample Size

1) In a poll to estimate presidential popularity, each person in a random sample of 1,000 voters was asked to agree with one of the following statements: 1. The President is doing a good job. 2. The President is doing a poor job. 3. I have no opinion. A total of 560 respondents selected the first statement, indicating

Hypothesis Testing, Confidence Intervals and ANOVA

1) The following is sample information. Test the hypothesis that the treatment mean are equal. Use the .05 significance level. Treatment 1 Treatment 2 Treatment 3 8 3 3 11 2 4 10 1 5 3 4 2 T1= 29 T2= 11 T3= 16 TOTAL T=56 N1= 3 N=5 N=4 N=12 9.6 (MEAN) 2.2 (MEAN) 4 (MEAN) 15.8 FOR GRAND MEAN A. State the

To find 99% confidence interval of mean difference in temperatures

The table gives the average low tempatures in January and July for twelve cities. Construct a 99% confidence interval for the mean temperature difference (January-July) between winter and summer. Assume the population are normally distributed. Cities JANUARY JULY Chhose the 99% confidence interval for the mean diffe

Law of Large Numbers

In regards to the stock market returns, what is the significance of the Law of Large Numbers? What do confidence intervals represent? What are the differences between z-statistics and t-statistics?

Determining a 99% Confidence Interval

a) A seed distributor guarantees 95% germination of the seeds he supplies. A retailer has an agreement with the distributor, under which he may test a random sample of 200 seeds for germination and send the whole batch back to the manufacturer if the proportion of germinating seeds is significantly below 95%. With a significance

Statistical Processes for Hypothesis Testing

(See attached file for full problem description with proper equations) An engineer was interested in comparing the variability of the power of a laser at current levels of 16 amps (X) and 20 amps (Y). To do so, random samples of 25 observations of power readings were obtained at each current level. The samples were taken hi

Application of Confidence Intervals

1. You are the manager of a tax preparation center. A vendor brings in a new software package that he says can reduce the amount of time spent preparing taxes. What would your null hypothesis be? With your null who is bearing the risk of Type I and Type II errors? 2. What is the value of establishing confidence intervals

Statistical processes

2. A company manufactures steel bolts that continuously feed an assembly line downstream. Historically, the thickness of these bolts follows a normal distribution with a standard deviation of 1.6 mm. A recent random sample of 10 observations yielded these values of thickness, in mm: 9.7 9.9 10.3 10.1 10.5 9.4 9.9 10.1

Hypothesis testing and confidence interval

Refer to the sample results below for the measured nicotine contents of randomly selected filtered and non-filtered king-size cigarettes. All measurements are in milligrams. a. use a 0.05 significance level to test the claim that king-size cigarettes with filters have a lower mean amount of nicotine than the mean amount of nic

Confidence interval for population variance

A discount store is trying to decide whether to use a single waiting line for available cashiers. The waiting times for 25 randomly selected customers was found to have a standard deviation of 1.7 minutes. Construct a 95% confidence interval for the population variance.

Confidence Intervals for Population

A College wished to know the number of library books borrowed by students over a term. 16 students were selected at random and the following data were obtained for the books they borrowed: 24, 22, 25, 25, 21, 26, 27, 22, 24, 23, 28, 23, 28, 25, 26, 21 (i) Calculate a 95% confidence interval for the population mean, . (ii)

Means and Confidence Intervals

8.54 Alice Chang and her colleagues (A. Chang, T. L. Rosenthal, R. H. Bryant, R. H. Rosenthal, R. M. Heidlage, and B. K. Fntzlcr. "Comparing High School and College Students' L.eisure In- wrests and Stress Ratings," Behavioral Research Therapy 31(2), 1993) tested 559 high school students using a leisure-interest checklist (LIC)


Smith Travel Research provides information on the one-night cost of hotel rooms throughout the United States (USA today, July 8, 2002). Use $2 as the desired margin of error and $22.50 as the planning value of the population standard deviation to find the sample size recommended in (a), (b), and (c). a. Determine a 90% confid

Confidence interval for blood pressure

Fifteen patients who suffer from high blood pressure were given a drug that is supposed to lower blood pressure. If X denotes the amount of a patient's decrease from his or her normal blood pressure and if the sample from 15 produced the estimate = 5 and s = 8, find a 95 percent confidence interval for using small sample meth

Confidence intervals

(See attached file for full problem description with proper symbols) --- Two sets of 100 students each were taught to read by two different methods. After instruction was over a reading test gave the following results: = 73.4, = 70.3, = 8, =10. Show that a 90 percent confidence interval for is

Calculate a 99 percent confidence interval for μ

The weight of a product is measured in pounds. A sample of 50 units is taken from a batch. The sample yielded the following results: = 75 lbs., and s = 10 lbs. Calculate a 99 percent confidence interval for μ.