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Confidence Interval

Solution to "Statistics - Confidence Interval" question

A random sample of 200 bolts from machine A contained 14 defective bolts, while an independently chosen, random sample of 325 bolts from machine B contained 35 defective bolts. Let P1 be the proportion of the population of all bolts from machine A that are defective, and let P2 be the proportion of the population of all bolts fr

Confidence Interval-difference between means (small sample)

The university data center has two main computers. The center wants to examine whether computer 1 is receiving tasks that require processing times comparable to those of computer 2. A random sample of 10 processing times from computer 1 showed a mean of 69 seconds with a standard deviation of 15 seconds, while a random sample of

The Sony corporation produces a Walkman that requires two AA Batteries. The mean life of these batteries in this product is 35.0 hours. The distribtion of the battery lives closely follows the normal probability distribtion with a standard deviation of 5.5 hours. As a part of their testing program Sony tests samples of 25 batteries. (1) What is the standard error of the distribution of the sample mean? (2) What proportion of the samples will have a mean useful life of more than 36 hours?

The Sony corporation produces a Walkman that requires two AA Batteries. The mean life of these batteries in this product is 35.0 hours. The distribtion of the battery lives closely follows the normal probability distribtion with a standard deviation of 5.5 hours. As a part of their testing program Sony tests samples of 25 batter

Sample Size, Margin of error

I) Find the minimum sample size you should use to assure that your estimate of p will be within the required margin of error around the population p. 1) margin of error:0.01; confidence level:95%; from a prior study p is estimated by the decimal equivalent of 55%. 2) Margin of error: 0.007; confidence level: 98%; p and q u

Calculation of confidence interval

Using the Central Limit Theorem. In Exercises 5-8, assume that women's height are normally distributed with a mean given by µ = 63.6 in. and a standard deviation given by σ = 2.5 (based on data from the National Health Survey). Sect. 6-5, p. 287 (For these problems, see examples on p. 283, 284 #5. a. If 1 wo

Sample size for estimating a population mean

An estimate is needed of the mean acreage of farms in Manitoba, Canada. The estimate should be correct to within 100 acres with probability 0.95. A preliminary study suggests that 500 acres is a reasonable guess for the standard deviation of farm size. How large a sample of farms is required and given that random sample size

Confidence Interval

Dave the jogger runs the same route every day (about 2.2 miles). On 18 consecutive days, he recorded the number of steps using a pedometer. The results were 3450 3363 3228 3360 3304 3407 3324 3365 3290 3289 3346 3252 3237 3210 3140 3220 3103 3129 Construct a 90 percent confidence interval for the true me

Confidence interval estimation for regression coefficients

1 What is the R^2 Value for your regression equation? 2 What is the value of the coefficient of Blue Collar in your equation? 3 What is the lower limit of the 95% CI for this coefficient? 4 What is the upper limit of the 95% CI for this coefficient?

Statistics

A supervisor for a large company wishes to estimate the proportion of parts from a supplier that are defective. He has selected a random sample of n = 200 incoming parts and has found 11 to be defective. Based on a 95% confidence level, the upper and lower limits for the confidence interval estimate are approximately 0.0234 to 0

Confidence interval and Hypothesis testing problems

Question 1: Confidence Interval for Effects of Marijuana Use on College Students: Data: Items sorted correctly by light marijuana users: n = 64, x = 53.3, s = 3.6 Items sorted correctly by heavy marijuana users: n = 65, x = 51.3, s = 4.5 Q: Refer to the sample data above and construct a 98% confidence interval fo

Confidence Interval for the True Mean

8.48 A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below: 0 26

Confidence interval estimation .

The security department of a state university is planning its budget for the next year. In estimating the man-hours for security during university sponsored music concerts, the average length of music concerts is needed. A random sample from thirty-six security departments at universities was taken and the sample mean length o

Benefits of Confidence Intervals

Please help with the following problem. Describe a business situation that you have had or might face that will benefit from the use of confidence intervals?

Sampling distribution of MEANS!

Let's say there is a local company (rhymes with "Zaplan") that promises a score of 625-good enough for admission to your favorite graduate school-if you take their $1200 preparatory course. 1. Treat yourself as a sample of 1 (N=1). Is a score of 625 significantly higher than average? Is it worth $800? Explain how you use a

Probability and confidence interval problems

A. Margaret Morris just correctly computed a standard deviation of 6.0 from a sample of 50 observations. What is the variance of Margaret's sample? b. Kim Fernando has just found the variance of a sample of 32 observations to be 64.0 by using a formula that is programmed into her new calculator. Therefore, what is the samp

Statistic Concepts: Estimates and Confidence

Part A: Define (a) point estimate, (b) interval estimate, (c) confidence interval, and (d) confidence level. Part B: List some common confidence levels. Why not use other confidence levels? Explain.

Defective Lightbulbs in a Given Shipments

A lightbulb manufacturer wants to estimate the total number of defective bulbs contained in all of the boxes shipped by the company during the past week. Production personnel at this company have recorded the number of defective bulbs found in each of 50 randomly selected boxes shipped during the past week. There data are provid

Confidence interval estimation problems

Please help with the following problem. Car Antifreeze: A container of car antifreeze is supposed to hold 3785mL of the liquid. Realizing that fluctuations are inevitable, the quality-control manager wants to be quite sure that the standard deviation is less than 30mL. Otherwise, some containers would overflow while other

Confidence Intervals and Limits for a Proportion Question

A survey of 85 families showed that 36 owned at least one DVD player. Find the 99% confidence interval estimate of the true proportion of families who own at least on DVD player. Place your limits, rounded to 3 decimal places, in the blanks. Simply provide the numerical values and decimal point if appicable. For example, 0.1

Confidence Interval Estimate for the population mean

A lawyer researched the average number of years served by 45 different justices on the Supreme Court. The average number of years served was 13.8 years with a standard deviation of 7.3 years. What is the 95% confidence interval estimate for the average number of years served by all Supreme Court justices? Rround to 1 decimal

Construction of 95 Percent Confidence Intervals

8.18 In a sample of 500 new Web sites registered on the Internet, 24 were anonymous (i.e., they shielded their name and contact information). (a) Construct a 95 percent confidence interval for the proportion of all new Web sites that were anonymous. 8.21 A 2003 survey showed that 4.6 percent of the 250 Americans surveyed

Confidence Intervals: Upper and Lower Limit

A sociologist is studying the prevalence of crime in one major city. In a sample of 225 randomly selected residents, 60 say that they have been victimized by a criminal. Based on this sample, construct a 95% confidence interval for the proportion of all residents in this city who have been victimized by a criminal. Then complete

Confidence interval for the population mean

A corporation that maintains a large fleet of company cars for the use of its sales staff is interested in the mean distance driven monthly per sales person. The following table gives the monthly distances in miles driven by a random sample of 20 sales persons 2314, 2102, 1999, 1951, 2602, 2468, 1881, 2381, 2230, 1966, 2246, 26

Constructing confidence intervals using data

A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below: 0 260 356 4

The upper limit of a 95% confidence interval for the population mean would equal? If the 10% level of significance ws used in testing the hypthesis H1o:u=201, H1" u = 201 the null hypothesis:

1) A random sample of size 15 taken from a normally distributed population revealed a sample mean of 75 and a sample variance of 25. The upper limit of a 95% confidence interval for the population mean would equal? 2. Based on sample data the 90% confidence interval limits forth population mean are 170.86 and 195.42. I

Statistics - Confidence Intervals and Standard Deviation

Please help with the following problems. Provide step by step calculations. 1. The security department of a university is planning its budget for the next year. in estimating the man-hours for security during university sponsored music concerts, the average length of music concerts is needed. A random sample from 36 secur

Understanding confidence intervals

What do we mean by confidence intervals - provide an example that illustrates your answer. Suppose we were to apply 95% and 99% confidence to your study results.. how might your result differ and why?