Q: Suppose you want to construct a 95% confidence interval for the mean resistance of circuits. You have a sample mean $$\bar{X} = 2.20$$ ohms, population standard deviation $$\sigma = 0.35$$ ohms, and sample size $$n = 11. $$What is the correct formula for the confidence interval?

$$2.20 \pm 1.96 \times \dfrac{0.35}{\sqrt{11}}$$

Q: Given a sample mean $$\bar{X} = 110.27$$, sample standard deviation $$S = 28.95$$, and sample size $$n = 100$$, what is the correct formula for a 95% confidence interval for the population mean using the t-distribution?

$$110.27 \pm t_{0.025,99} \times \dfrac{28.95}{\sqrt{100}}$$

Q: A sample of size $$n = 25 is $$taken from a population with $$\mu = 368$$ and $$\sigma = 15. $$What is the 95% confidence interval for the population mean?

$$(368 - 1.96 \times \dfrac{15}{\sqrt{25}},\ 368 + 1.96 \times \dfrac{15}{\sqrt{25}})$$

Question 1

Which of the following best describes a point estimate in statistics?

Accepted Answer

A single value calculated from a sample used to estimate a population parameter.

Question 2

A confidence interval provides which of the following advantages over a point estimate?

Accepted Answer

It gives a range of values, reflecting the precision and uncertainty of the estimate.

Question 3

Suppose you want to construct a 95% confidence interval for the mean resistance of circuits. You have a sample mean $$\bar{X} = 2.20$$ ohms, population standard deviation $$\sigma = 0.35$$ ohms, and sample size $$n = 11. $$What is the correct formula for the confidence interval?

Accepted Answer

$$2.20 \pm 1.96 	imes \dfrac{0.35}{\sqrt{11}}$$

Question 4

If the population standard deviation is unknown and the sample size is small ($$n \u003c 30$$), which distribution should be used to construct a confidence interval for the mean?

Accepted Answer

Student's t distribution

Question 5

Which of the following statements about confidence intervals is TRUE?

Accepted Answer

A 95% confidence interval means that 95% of intervals constructed from repeated samples will contain the true parameter.

Question 6

Given a sample mean $$\bar{X} = 110.27$$, sample standard deviation $$S = 28.95$$, and sample size $$n = 100$$, what is the correct formula for a 95% confidence interval for the population mean using the t-distribution?

Accepted Answer

$$110.27 \pm t_{0.025,99} 	imes \dfrac{28.95}{\sqrt{100}}$$

Question 7

Which of the following is NOT an assumption for constructing a confidence interval for the mean when the population standard deviation is known?

Accepted Answer

The population standard deviation is unknown.

Question 8

A company wants to estimate the proportion of defective products. Which formula should be used to construct a confidence interval for the population proportion $$\pi$$?

Accepted Answer

$$\hat{p} \pm Z_{\alpha/2} \sqrt{\dfrac{\hat{p}(1-\hat{p})}{n}}$$

Question 9

If you increase the confidence level from 95% to 99%, what happens to the width of the confidence interval?

Accepted Answer

The width increases.

Question 10

A sample of size $$n = 25 is $$taken from a population with $$\mu = 368$$ and $$\sigma = 15. $$What is the 95% confidence interval for the population mean?

Accepted Answer

$$(368 - 1.96 	imes \dfrac{15}{\sqrt{25}},\ 368 + 1.96 	imes \dfrac{15}{\sqrt{25}})$$

Question 11

Which of the following best explains why we use the t-distribution instead of the normal distribution for small samples?

Accepted Answer

The t-distribution accounts for the additional uncertainty in estimating the population standard deviation from the sample.

Question 12

A researcher calculates a 90% confidence interval for the mean. What is the value of $$Z_{\alpha/2}$$ used in the calculation?

Accepted Answer

$$1.645$$

Question 13

Which of the following is a correct interpretation of a 99% confidence interval for a population mean?

Accepted Answer

99% of all possible confidence intervals constructed from repeated samples will contain the true population mean.

Question 14

A sample of 100 travel times has a mean of 110.27 minutes and a standard deviation of 28.95 minutes. The critical value for a 95% confidence interval with 99 degrees of freedom is $$t_{0.025,99} = 1.9842. $$What is the margin of error?

Accepted Answer

$$1.9842 	imes \dfrac{28.95}{\sqrt{100}}$$

Question 15

Which of the following factors will NOT affect the width of a confidence interval for the mean?

Accepted Answer

Sample mean value

Question 16

A business analyst wants to be more certain that their confidence interval contains the true mean. What should they do?

Accepted Answer

Increase the confidence level (e.g., from 95% to 99%).

Question 17

If a confidence interval for the mean is $$(1.99, 2.41)$$ ohms, which of the following is the correct interpretation?

Accepted Answer

We are 95% confident that the true mean resistance is between 1.99 and 2.41 ohms.

Question 18

Which of the following is the general formula for a confidence interval for a population parameter?

Accepted Answer

$$	ext{Point Estimate} \pm 	ext{Critical Value} 	imes 	ext{Standard Error}$$

Confidence Intervals and Estimation (Statistics for Business)

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