Chapter 11: Problem 10
Explain the difference between the observed and expected frequencies for a goodness-of-fit test.
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Chapter 11: Problem 10
Explain the difference between the observed and expected frequencies for a goodness-of-fit test.
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Sandpaper is rated by the coarseness of the grit on the paper. Sandpaper that is more coarse will remove material faster. Jobs such as the final sanding of bare wood prior to painting or sanding in between coats of paint require sandpaper that is much finer. A manufacturer of sandpaper rated 220, which is used for the final preparation of bare wood, wants to make sure that the variance of the diameter of the particles in their 220 sandpaper does not exceed \(2.0\) micrometers. Fifty-one randomly selected particles are measured. The variance of the particle diameters is \(2.13\) micrometers. Assume that the distribution of particle diameter is approximately normal. a. Construct the \(95 \%\) confidence intervals for the population variance and standard deviation. b. Test at a \(2.5 \%\) significance level whether the variance of the particle diameters of all particles in 220-rated sandpaper is greater than \(2.0\) micrometers.
Of all students enrolled at a large undergraduate university, \(19 \%\) are seniors, \(23 \%\) are juniors, \(27 \%\) are sophomores, and \(31 \%\) are freshmen. A sample of 200 students taken from this university by the student senate to conduct a survey includes 50 seniors, 46 juniors, 55 sophomores, and 49 freshmen. Using a \(2.5 \%\) significance level, test the null hypothesis that this sample is a random sample. (Hint: This sample will be a random sample if it includes approximately \(19 \%\) seniors, \(23 \%\) juniors, \(27 \%\) sophomores, and \(31 \%\) freshmen.)
A sample of 25 observations selected from a normally distributed population produced a sample variance of \(35 .\) Construct a confidence interval for \(\sigma^{2}\) for each of the following confidence levels and \(\mathrm{com}-\) ment on what happens to the confidence interval of \(\sigma^{2}\) when the confidence level decreases. a. \(1-\alpha=.99\) b. \(1-\alpha=.95\) c. \(1-\alpha=.90\)
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