Questions: A state legislator wants to determine whether his voters' performance rating (0-100) has changed from last year to this year. The following table shows the legislator's performance from the same ten randomly selected voters for last year and this year. Use this data to find the 90% confidence interval for the true difference between the population means. Assume that the populations of voters' performance ratings are normally distributed for both this year and last year. Rating (last year) 75 80 75 74 88 79 53 63 69 78 Rating (this year) 85 69 54 63 63 91 58 52 89 72

A state legislator wants to determine whether his voters' performance rating (0-100) has changed from last year to this year. The following table shows the legislator's performance from the same ten randomly selected voters for last year and this year. Use this data to find the 90% confidence interval for the true difference between the population means. Assume that the populations of voters' performance ratings are normally distributed for both this year and last year.

Rating (last year)  75  80  75  74  88  79  53  63  69  78

Rating (this year)  85  69  54  63  63  91  58  52  89  72
Transcript text: A state legislator wants to determine whether his voters' performance rating ( $0-100$ ) has changed from last year to this year. The following table shows the legislator's performance from the same ten randomly selected voters for last year and this year. Use this data to find the $90 \%$ confidence interval for the true difference between the population means. Assume that the populations of voters' performance ratings are normally distributed for both this year and last year. \begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|} \hline Rating (last year) & 75 & 80 & 75 & 74 & 88 & 79 & 53 & 63 & 69 & 78 \\ \hline Rating (this year) & 85 & 69 & 54 & 63 & 63 & 91 & 58 & 52 & 89 & 72 \\ \hline \end{tabular}
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Solution

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Solution Steps

Step 1: Calculate Paired Differences

The paired differences between this year's and last year's ratings are calculated as follows:

\[ \text{Paired differences} = [10, -11, -21, -11, -25, 12, 5, -11, 20, -6] \]

Step 2: Calculate the Mean of the Paired Differences

The mean \(\mu\) of the paired differences is calculated using the formula:

\[ \mu = \frac{\sum x_i}{n} = \frac{-38}{10} = -3.8 \]

Step 3: Calculate the Variance

The variance \(\sigma^2\) of the paired differences is calculated using the formula:

\[ \sigma^2 = \frac{\sum (x_i - \mu)^2}{n-1} = 221.066667 \]

Step 4: Calculate the Standard Deviation

The sample standard deviation \(s\) is calculated as follows:

\[ s = \sqrt{221.066667} = 14.868311 \]

Final Answer

The sample standard deviation of the paired differences is

\[ \boxed{14.868311} \]

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