Exam 11: Estimation: Describing a Single Population

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Suppose that the amount of time teenagers spend on the Internet is normally distributed, with a standard deviation of 1.5 hours. A sample of 100 teenagers is selected at random, and the sample mean is computed as 6.5 hours. Determine the 95% confidence interval estimate of the population mean, changing the sample mean to 8.5 hours.

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As the number of degrees of freedom for a t-distribution increases: A the dispersion of the distribution decreases. B the shape of the distribution becomes narrower and taller. C the t -distribution becomes more and more similar to the standard normal distribution. D All of these choices are correct.

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Suppose that the amount of time teenagers spend on the Internet is normally distributed, with a standard deviation of 1.5 hours. A sample of 100 teenagers is selected at random, and the sample mean is computed as 6.5 hours. Determine the 95% confidence interval estimate of the population mean, changing the sample mean to 5.0 hours.

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In developing an interval estimate for a population mean, the population standard deviation σ\sigma was assumed to be 8. The interval estimate was 50.0 ± 2.50. Had σ\sigma equalled 16, the interval estimate would have been 100 ± 5.0.

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The sample proportion is a biased estimator of the population proportion.

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Suppose that the amount of time teenagers spend on the Internet is normally distributed, with a standard deviation of 1.5 hours. A sample of 100 teenagers is selected at random, and the sample mean is computed as 6.5 hours. Determine the 95% confidence interval estimate of the population mean, changing the sample size to 36.

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Which of the following best describes an interval estimator? α\alpha A An interval estimator is the same as a point estimator. B An interval estimator is an interval that draws inferences about a population based on a sample statistic. C An interval estimator can only be done for the population mean. D An interval estimator can only be done for the population proportion.

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If the standard error of the sampling distribution of the sample proportion is 0.0337 for samples of size 200, then the population proportion must be: A. 0.25. B. 0.75. C. either 0.20 or 0.80 D. either 0.35 or 0.65 E. either 0.30 or 0.70

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The degrees of freedom used to find the t/2 for a confidence interval for the population mean? A The degrees of freedom are n-2 . B The degrees of freedom are n-3 . C The degrees of freedom are n-1 . D The degrees of freedom are n .

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A random sample of size 20 taken from a normally distributed population resulted in a sample variance of 32. The lower limit of a 90% confidence interval for the population variance would be: A. 52.185. B. 20.375. C. 20.170. D. 54.931.

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We cannot interpret the confidence interval estimate of μ\mu as a probability statement about μ\mu , simply because the population mean is a fixed but unknown quantity.

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The sample proportion p^\hat { p } is a consistent estimator of the population proportion p because it is unbiased and the variance of p^\hat { p } is p(1 - p)/n, which grows smaller as n grows larger.

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