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12 votes
12 votes
Tara keeps track of the numbers of trips she takes to the library into the bookstore each month for a year. Her data are shown in the scatterplot below. Which equation represents a line of best fit for the date in the scatterplot? Is the correct answer ABC or D?

Tara keeps track of the numbers of trips she takes to the library into the bookstore-example-1
User Sergey Krusch
by
2.8k points

1 Answer

19 votes
19 votes

12 points are given on the plane


\lbrace(1,6),(2,6),(2,5),(2,3),(3,5),(3,2),(4,4),(4,3),(4,1),(5,1),(6,1),(7,1)\rbrace

Finding the mean of X and Y,


\begin{gathered} M_x=(1+2+2+2+3+3+4+4+4+5+6+7)/(12)=3.5833 \\ and \\ M_y=(6+6+5+3+5+2+4+3+1+1+1+1)/(12)=3.4167 \end{gathered}

Then, the sum of squares and the sum of products,


\begin{gathered} SS_x=\sum_{n\mathop{=}0}^(12)(x_n-M_x)^2=34.9167 \\ and \\ S_(xy)=\sum_{n\mathop{=}0}^(12)(x_n-M_x)(y_n-M_y)=-23.9167 \end{gathered}

x_n and y_n are the x and y

In general, the linear regression equation is given by the formula below


\begin{gathered} y=bX+a \\ b=(S_(xy))/(SS_x) \\ and \\ a=M_y-bM_x \end{gathered}

Therefore, in our case, calculating a and b,


\begin{gathered} b=-(23.9167)/(34.9167)=-0.68496 \\ and \\ a=3.4167-(-0.68496)*3.5833=5.87112 \end{gathered}

Thus, the line of best fit is


\Rightarrow y=-0.68496x+5.89112

Hence, the option that more resemble the equation above is the last option. The answer is y=-2x/3+6 2/3

User David Hansen
by
2.9k points
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