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20 questions for XXIAO only

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Question 1 of 20

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Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), "E" or "e" (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker.
Complex numbers should be in the form (a + bi) where "a" and "b" need to have explicitly stated values.
For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not.

A sample of 9 production managers with over 15 years of experience has an average salary of $71,000 and a sample standard deviation of $18,000.

Assuming that the salaries of production managers with over 15 years experience are normally distributed, you can be 95% confident that the mean salary for all production managers with at least 15 years of experience is between what two numbers.

Place your LOWER limit, rounded to a whole number, in the first blank. Do not use a dollar sign, a comma, or any other stray mark. For example, 54321 would be a legitimate entry.

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Question 9 of 20

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From a sample of 500 items, 30 were found to be defective. The point estimate of the population proportion defective will be:

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Question 10 of 20

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Find the 95% confidence interval for the standard deviation of the lengths of pipes if a sample of 26 pipes has a standard deviation of 10 inches.

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Question 11 of 20

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Compute $f$P(t_{20}leq -0.95)f$$ where t₂₀ has a t-distribution with 20 degrees of freedom.

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Question 12 of 20

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Which of the following will make a confidence interval narrower and more precise?

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Question 13 of 20

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A sample of 23 European countries found that the variance of life expectancy was 7.3 years. What is the 95% confidence interval estimate for the variance of life expectancy in Europe?

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Question 14 of 20

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The t- distribution for developing a confidence interval for a mean has _____ degrees of freedom.

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Question 15 of 20

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If you are constructing a confidence interval for a single mean, the confidence interval will___________ with an increase in the sample size.

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Question 16 of 20

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Confidence intervals are a function of which of the following three things?

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Question 17 of 20

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If you increase the confidence level, the confidence interval ____________.

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Question 18 of 20

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The average gas mileage of a certain model car is 26 miles per gallon. If the gas mileages are normally distributed with a standard deviation of 1.3, find the probability that a randomly selected car of this model has a gas mileage between 25.8 and 26.3 miles per gallon.

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Part 3 of 3 -

Question 19 of 20

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The lower limit of the 95% confidence interval for the population proportion p, given that n = 300; and $f$hat{p}f$$ = 0.10 is 0.1339.

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Question 20 of 20

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A 90% confidence interval estimate for a population mean is determined to be 72.8 to 79.6. If the confidence level is reduced to 80%, the confidence interval becomes narrower.

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