Exam 9: Sampling Distributions

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NARRBEGIN: Heights of Fences Heights of Fences Heights of fences are normally distributed with a mean of 52 inches and a standard deviation of 4 inches.NARREND -{Heights of Fence Narrative} Find the probability that the mean height of 4 randomly selected fences is under 54 inches.

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Which of the following is true regarding the sampling distribution of the mean for a large sample size? Assume the population distribution is not normal.

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If a simple random sample of 300 observations is taken from a population whose proportion p = 0.6, then the expected value of the sample proportion p~\tilde{ p } is 0.60.

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As n gets larger, the sampling distribution of Xˉ\bar { X } becomes increasingly bell shaped. This phenomenon is due to the ____________________.

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A randomly selected value of Xˉ\bar { X } is likely to be ____________________ to(than) the mean of the population than is a randomly selected value of X.

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Under certain conditions where n is large enough, you can approximate the ____________________ distribution using the ____________________ distribution.

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The width of the sampling distribution of Xˉ\bar { X } gets ____________________ as the sample size increases.

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As a general rule, the normal distribution is used to approximate the sampling distribution of the sample proportion only if:

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The amount of bleach a machine pours into bottles has a mean of 50 ounces with a standard deviation of 0.25 ounces. Suppose we take a random sample of 36 bottles filled by this machine. The sampling distribution of the sample mean has a standard error of 0.25 ounces.

(True/False)
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NARRBEGIN: DVD Rental Store DVD Rental Store A DVD rental store wants to know what proportion of its customers are under age 21. A simple random sample of 500 customers was taken, and 375 of them were under age 21. Presume that the true population proportion of customers under age 21 is 0.68.NARREND -{DVD Rental Store Narrative} What is the probability that the sample proportion p~\tilde{ p } is within 0.03 of the true proportion of customers who are under age 21?

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The Central Limit Theorem states that, if a random sample of size n is drawn from a population, then the sampling distribution of the sample mean Xˉ\bar { X } :

(Multiple Choice)
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NARRBEGIN: Number of Fish Tanks Number of Fish Tanks The following data give the number of fish tanks owned for a population of 4 families. Family A B C D Number af Fish Tanks Owned 2 1 4 3 NARREND -{Number of Fish Tanks Narrative} A sample of size 2 is drawn at random from the population. Use the formulas μxˉ=μ\mu _ { \bar { x } } = \mu and σxˉ=σnNnN1\sigma _ { \bar { x } } = \frac { \sigma } { \sqrt { n } } \sqrt { \frac { N - n } { N - 1 } } to calculate the mean and the standard deviation of the sampling distribution of the sample means.

(Essay)
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Recall the rule of thumb used to indicate when the normal distribution is a good approximation of the sampling distribution for the sample proportion p~\tilde{ p } . For the combination n = 50, p = 0.05, the rule is satisfied.

(True/False)
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If two populations are normally distributed, the sampling distribution of the difference in the sample means, Xˉ1Xˉ2\bar { X } _ { 1 } - \bar { X } _ { 2 } , is:

(Multiple Choice)
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The Central Limit Theorem permits us to draw conclusions about a population based on a sample alone, without having any knowledge about the distribution of that population. And this works no matter what the sample size is.

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Suppose it is known that 60% of radio listeners at a particular college are smokers. A sample of 500 students from the college is selected at random. Approximate the probability that at least 280 of these students are radio listeners.

(Short Answer)
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The probability of success on any trial of a binomial experiment is 20%. Find the probability that the proportion of success in a sample of 400 is: a.less than 18%. b.more than 18%. c.between 18% and 22%.

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The variance of the sampling distribution of Xˉ\bar { X } is ____________________ the variance of the population we're sampling from, for any n > 1.

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NARRBEGIN: Magazines Magazines A local magazine store sells an average of 2,100 magazines per day, with a standard deviation of 500 magazines. Consider a sample of 60 days of operation.NARREND -{Magazines Narrative} Find the expected value and the standard error of the sample mean.

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Suppose X has a distribution that is not normal. The Central Limit Theorem is important in this case because:

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