Chapter 6: Problem 3
What is a population parameter? Give three examples.
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Chapter 6: Problem 3
What is a population parameter? Give three examples.
These are the key concepts you need to understand to accurately answer the question.
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A person's blood glucose level and diabetes are closely related. Let \(x\) be a random variable measured in milligrams of glucose per deciliter \((1 / 10 \text { of a liter })\) of blood. After a 12 -hour fast, the random variable \(x\) will have a distribution that is approximately normal with mean \(\mu=85\) and standard deviation \(\sigma=25\) (Source: Diagnostic Tests with Nursing Implications, edited by S. Loeb, Springhouse Press). Note: After 50 years of age, both the mean and standard deviation tend to increase. What is the probability that, for an adult (under 50 years old) after a 12 -hour fast, (a) \(x\) is more than \(60 ?\) (b) \(x\) is less than \(110 ?\) (c) \(x\) is between 60 and \(110 ?\) (d) \(x\) is greater than 125 (borderline diabetes starts at 125 )?
Find the indicated probability, and shade the corresponding area under the standard normal curve. $$P(-0.73 \leq z \leq 3.12)$$
Find the \(z\) value described and sketch the area described.Find the \(z\) value such that \(98 \%\) of the standard normal curve lies between \(-z\) and \(z\).
Does a raw score less than the mean correspond to a positive or negative standard score? What about a raw score greater than the mean?
Let \(x\) represent the dollar amount spent on supermarket impulse buying in a 10 -minute (unplanned) shopping interval. Based on a Denver Post article, the mean of the \(x\) distribution is about \(\$ 20\) and the estimated standard deviation is about \(\$ 7\) (a) Consider a random sample of \(n=100\) customers, each of whom has 10 minutes of unplanned shopping time in a supermarket. From the central limit theorem, what can you say about the probability distribution of \(\bar{x}\) the average amount spent by these customers due to impulse buying? What are the mean and standard deviation of the \(\bar{x}\) distribution? Is it necessary to make any assumption about the \(x\) distribution? Explain. (b) What is the probability that \(\bar{x}\) is between \(\$ 18\) and \(\$ 22 ?\) (c) Let us assume that \(x\) has a distribution that is approximately normal. What is the probability that \(x\) is between \(\$ 18\) and \(\$ 22 ?\) (d) Interpretation: In part (b), we used \(\bar{x},\) the average amount spent, computed for 100 customers. In part (c), we used \(x,\) the amount spent by only one customer. The answers to parts (b) and (c) are very different. Why would this happen? In this example, \(\bar{x}\) is a much more predictable or reliable statistic than \(x\). Consider that almost all marketing strategies and sales pitches are designed for the average customer and not the individual customer. How does the central limit theorem tell us that the average customer is much more predictable than the individual customer?
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