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Chapter 8: Q.9 (page 482)

How confident? The figure below shows the result of taking 25SRSs from a Normal population and constructing a confidence interval for each sample. Which confidence level—80%,90%,95%, or 99%— do you think was used? Explain

Short Answer

Expert verified

The nearest confidence level is 80%.

Step by step solution

01

Given Information

The result of 25SRSs:

02

Explanation

The red lines under the curve represent the sample means that does not contain the true population mean μ.

We note that there are 4out of the 25samples that do not contain the true proportion and thus 21out of the 25samples contain the true mean:

2125=0.84=84%

The nearest confidence level is 80%

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Most popular questions from this chapter

Critical value What critical value t*from Table B would you use for a 90%confidence interval for the population mean based on an SRS of size 77? If possible, use technology to find a more accurate value of . What advantage does the more accurate df provide?

The Gallup Poll interviews 1600people. Of these, 18%say that they jog regularly. The news report adds: "The poll had a margin of error of plus or minus three percentage points at a 95%confidence level." You can safely conclude that

(a) 95%of all Gallup Poll samples like this one give answers within±3%of the true population value.

(b) the percent of the population who jog is certain to be between 15%and21%.

(c) 95%of the population jog between5%and21%of the time.

(d) we can be 95%confident that the sample proportion is captured by the confidence interval.

(e) if Gallup took many samples,95%of them would find that 18%of the people in the sample jog.

Good wood? A lab supply company sells pieces of Douglas fir 4inches long and 1.5inches square for force experiments in science classes. From experience, the strength of these pieces of wood follows a Normal distribution with standard deviation 3000pounds. You want to estimate the mean load needed to pull apart these pieces of wood to within 1000pounds with 95%confidence. How large a sample is needed? Show your work.

- Understand how the margin of error of a confidence interval changes with the sample size and the level of confidence C.

NAEP scores Refer to Exercise 5. Below your sketch, choose one value of x inside the shaded region and draw its corresponding confidence interval. Do the same for one value of x outside the shaded region. What is the most important difference between these intervals?

An online poll posed the following question:

It is now possible for school students to log on to Internet sites and download homework. Everything from book reports to doctoral dissertations can be downloaded free or for a fee. Do you believe that giving a student who is caught plagiarizing an F for their assignment is the right punishment?

Of the 20,125people who responded, 14,793clicked “Yes.” That’s 73.5%of the sample. Based on this sample, a 95%confidence interval for the percent of the population who would say “Yes” is 73.5% ±0.61. Which of the three inference conditions is violated? Why is this confidence interval worthless?
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