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Chapter 7: Q.66 (page 456)
The standard deviation of the average scores you get should be close to
(a) .
(b) .
(c) .
(d) .
(e) none of these.
The average score's standard deviation is.
The correct answer is (c).
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The CLT applet Go to the textbook Web site (www whfreeman com/tp4e) and click on "Statistical Applets." Launch the Central limit Theorem applet. You should see a screen like the one shown here. Click and drag the slider to change the sample size, and watch how the density curve for the sampling distribution changes with it. Write a few sentences describing what in happening.
You work for an advertising agency that is preparing a new television commercial to appeal to women. You have been asked to design an experiment to compare the effectiveness of three versions of the commercial. Each subject will be shown one of the three versions and then asked about her attitude toward the product. You think there may be large differences between women who are employed and those who are not. Because of these differences, you should use
(a) a block design, but not a matched pairs design
(b) a completely randomized design.
(c) a matched pairs design.
(d) a simple random sample.
(e) a stratified random sample.
The gypsy moth is a serious threat to oak and aspen trees. A state agriculture department places traps throughout the state to detect the moths. When traps are checked periodically, the mean number of moths trapped is only but some traps have several moths. The distribution of moth counts is discrete and strongly skewed, with standard deviation.
(a) What are the mean and standard deviation of the average number of moths intraps?
(b) Use the central limit theorem to help you find the probability that the average number of moths in traps is greater than.
Social scientists are interested in the association between the high school graduation rate (HSGR) and the percentage of U.S. families living in poverty (POV). Data were collected from all states and the District of Columbia, and a regression analysis was conducted. The resulting least-squares regression line is given by (HSGR) with . Based on the information, which of the following is the best interpretation for the slope of the least-squares regression line?
(a) For each increase in the graduation rate, the per cent of families living in poverty is predicted to decrease by approximately .
(b) For each increase in the graduation rate, the per cent of families living in poverty is predicted to decrease by approximately .
(c) For each increase in the graduation rate, the per cent of families living in poverty is predicted to decrease by approximately .
(d) For eachincrease in the percentage of families living in poverty, the graduation rate is predicted to increase by approximately .
(e) For each increase in the per cent of families living in poverty, the graduation rate is predicted to decrease by approximately.
The histogram above left shows the intervals (in minutes) between eruptions of the Old Faithful geyser for all recorded eruptions during a particular month. For this population, the median is minutes. We used Fathom software to take SRSs of size from the population. The values of the sample median are displayed in the histogram above right. The mean of the sample median values is 73.5.
Is the sample median an unbiased estimator of the population median? Justify your answer
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