Problem

The following data represent the age (in weeks) at which babies first crawl based on a survey of 12 mothers. The data are normally distributed and s=10.103 weeks. Construct and interpret a 95\% confidence interval for the population standard deviation of the age (in weeks) at which babies first crawl.
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Click the icon to view the table of critical values of the chi-square distribution.
Select the correct choice below and fill in the answer boxes to complete your choice. (Use ascending order. Round to three decimal places as needed.)
A. There is a 95% probability that the true population standard deviation is between and
B. There is 95% confidence that the population standard deviation is between and
C. If repeated samples are taken, 95% of them will have the sample standard deviation between and

Answer

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Answer

Final Answer: There is 95% confidence that the population standard deviation is between 7.157 and 17.154.

Steps

Step 1 :Given that the sample size (n) is 12 and the sample standard deviation (s) is 10.103 weeks. We are asked to construct a 95% confidence interval for the population standard deviation.

Step 2 :First, we calculate the degrees of freedom (df) which is given by n - 1. So, df = 12 - 1 = 11.

Step 3 :Next, we calculate the critical values of the chi-square distribution. The lower critical value (χα/22) is found at the α/2 quantile and the upper critical value (χ1α/22) is found at the 1α/2 quantile of the chi-square distribution with df degrees of freedom. Here, α is 0.05, so α/2 is 0.025.

Step 4 :Using a chi-square table or a statistical software, we find that χα/22 = 3.816 and χ1α/22 = 21.920.

Step 5 :Then, we calculate the confidence interval for the population standard deviation. The lower bound is given by (df×s2)/χ1α/22 and the upper bound is given by (df×s2)/χα/22.

Step 6 :Substituting the given values, we get the lower bound as (11×(10.103)2)/21.920 = 7.157 and the upper bound as (11×(10.103)2)/3.816 = 17.154.

Step 7 :Final Answer: There is 95% confidence that the population standard deviation is between 7.157 and 17.154.

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