High School

A construction manager is monitoring the progress of building a new house. The scatterplot and table show the number of months since the start of the build and the percentage of the house still left to build. A linear function can be used to model this relationship.

[tex]
\[
\begin{array}{|c|c|}
\hline
\text{Number of Months Since Start of Build, } x & \text{Percentage of House Left to Build, } y \\
\hline
0 & 100 \\
\hline
1 & 86 \\
\hline
2 & 65 \\
\hline
3 & 59 \\
\hline
4 & 41 \\
\hline
5 & 34 \\
\hline
\end{array}
\]
[/tex]

Which function best models the data?

A. [tex]y = -13.5x + 97.8[/tex]

B. [tex]y = -13.5x + 7.3[/tex]

C. [tex]y = 97.8x - 13.5[/tex]

D. [tex]y = 7.3x - 97.8[/tex]

Answer :

We want to find a linear function of the form

[tex]$$
y = m x + b,
$$[/tex]

where [tex]$m$[/tex] is the slope and [tex]$b$[/tex] is the [tex]$y$[/tex]-intercept. The data given is:

[tex]\[
\begin{array}{c|c}
x & y \\
\hline
0 & 100 \\
1 & 86 \\
2 & 65 \\
3 & 59 \\
4 & 41 \\
5 & 34 \\
\end{array}
\][/tex]

Step 1. Compute the slope [tex]$m$[/tex].

The formula for the slope is

[tex]$$
m = \frac{\sum (x - \bar{x})(y - \bar{y})}{\sum (x - \bar{x})^2},
$$[/tex]

where [tex]$\bar{x}$[/tex] and [tex]$\bar{y}$[/tex] are the averages of the [tex]$x$[/tex] and [tex]$y$[/tex] values respectively.

After performing the calculations, the slope is found to be approximately

[tex]$$
m \approx -13.46.
$$[/tex]

Step 2. Compute the [tex]$y$[/tex]-intercept [tex]$b$[/tex].

Once the slope is determined, the [tex]$y$[/tex]-intercept can be calculated using the formula

[tex]$$
b = \bar{y} - m\bar{x}.
$$[/tex]

With the computed values, the intercept is approximately

[tex]$$
b \approx 97.81.
$$[/tex]

Step 3. Formulate the linear equation.

Substituting the values of [tex]$m$[/tex] and [tex]$b$[/tex] into the linear equation gives

[tex]$$
y \approx -13.46\,x + 97.81.
$$[/tex]

Rounding the slope to [tex]$-13.5$[/tex] and the intercept to [tex]$97.8$[/tex], the equation becomes

[tex]$$
y = -13.5\,x + 97.8.
$$[/tex]

Step 4. Identify the correct model.

Comparing with the answer choices:

[tex]\[
\begin{aligned}
\textbf{A: } & y=-13.5 x+97.8 \\
\textbf{B: } & y=-13.5 x+7.3 \\
\textbf{C: } & y=97.8 x-13.5 \\
\textbf{D: } & y=7.3 x-97.8
\end{aligned}
\][/tex]

we see that the equation we obtained, [tex]$y=-13.5 x+97.8$[/tex], corresponds to option A.

Final Answer: Option A.

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