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The following table gives retail values of a 2020 Corvette for various odometer readings.

[tex]
\[
\begin{tabular}{|c|c|}
\hline
Odometer Reading & Retail Value (\$) \\
\hline
13,000 & 52,525 \\
\hline
18,000 & 51,625 \\
\hline
20,000 & 51,350 \\
\hline
25,000 & 50,325 \\
\hline
29,000 & 49,875 \\
\hline
32,000 & 49,225 \\
\hline
\end{tabular}
\]
[/tex]

(a) Find the equation of the least-squares line for the data. (Where odometer reading is the independent variable, [tex]$x$[/tex], and retail value is the dependent variable. Round your numerical values to two decimal places.)

[tex]\hat{y} = \square[/tex]

(b) Use the equation from part (a) to predict the retail price of a 2020 Corvette with an odometer reading of 30,000. Round to the nearest [tex]$100.[/tex]

[tex]\$[/tex] \square

(c) Find the linear correlation coefficient for these data. (Round your answer to four decimal places.)

[tex]r = \square[/tex]

(d) What is the significance of the fact that the linear correlation coefficient is negative for these data?

The variables are negatively correlated, which means that as the odometer reading goes up, the retail value goes down.

Answer :

We are given the following data for odometer readings ([tex]$x$[/tex]) and retail values ([tex]$y$[/tex]):

[tex]\[
\begin{array}{|c|c|}
\hline
\text{Odometer Reading } (x) & \text{Retail Value } (y) \\
\hline
13000 & 52525 \\
\hline
18000 & 51625 \\
\hline
20000 & 51350 \\
\hline
25000 & 50325 \\
\hline
29000 & 49875 \\
\hline
32000 & 49225 \\
\hline
\end{array}
\][/tex]

We now explain the steps for finding the answers.

──────────────────────────────
Step (a): Least-Squares Line

To find the least-squares line of the form

[tex]\[
\hat{y} = a + b x,
\][/tex]

we compute the slope [tex]$b$[/tex] and intercept [tex]$a$[/tex] using the standard formulas:

[tex]\[
b = \frac{n\sum (xy) - \left(\sum x\right)\left(\sum y\right)}{n\sum{x^2} - \left(\sum x\right)^2}, \quad
a = \overline{y} - b \, \overline{x},
\][/tex]

where [tex]$n$[/tex] is the number of data points.

After carrying out the computations and rounding the values to two decimal places, the resulting equation is

[tex]\[
\hat{y} = 54734.53 - 0.17 x.
\][/tex]

Since this is a linear equation, the degree of the polynomial is 1.

──────────────────────────────
Step (b): Predicting the Retail Value at 30000 Miles

To predict the retail value when the odometer reading is [tex]$x = 30000$[/tex], substitute into the equation:

[tex]\[
\hat{y} = 54734.53 - 0.17(30000).
\][/tex]

Performing the multiplication:

[tex]\[
0.17 \times 30000 = 5100,
\][/tex]

so

[tex]\[
\hat{y} \approx 54734.53 - 5100 = 49634.53.
\][/tex]

Rounding to the nearest \[tex]$100 gives a predicted value of

\[
\$[/tex]49600.
\]

──────────────────────────────
Step (c): Linear Correlation Coefficient

The linear correlation coefficient [tex]$r$[/tex] is calculated by

[tex]\[
r = \frac{\sum \left(x - \overline{x}\right)\left(y - \overline{y}\right)}{\sqrt{\sum \left(x - \overline{x}\right)^2 \sum \left(y - \overline{y}\right)^2}}.
\][/tex]

After doing the appropriate computations and rounding to four decimal places, we obtain

[tex]\[
r = -0.9979.
\][/tex]

──────────────────────────────
Step (d): Interpretation of the Negative Correlation

A negative linear correlation coefficient indicates that as the odometer reading increases, the retail value of the vehicle tends to decrease. In other words, higher mileage is associated with a lower retail value.

──────────────────────────────
Summary of Answers

(a) The equation of the least-squares line is

[tex]\[
\hat{y} = 54734.53 - 0.17x \quad (\text{with a polynomial degree of } 1).
\][/tex]

(b) For an odometer reading of [tex]$30000$[/tex], the predicted retail value is approximately

[tex]\[
\$49600.
\][/tex]

(c) The linear correlation coefficient is

[tex]\[
r = -0.9979.
\][/tex]

(d) The negative correlation coefficient means that as the odometer reading increases, the retail value decreases.

These are the detailed steps and results for this problem.

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