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The table shown below gives the national average pupil-teacher ratio in public schools over selected years.

\begin{array}{|c|c|}
\hline \text { Year } & \text { Ratio } \\
\hline 1992 & 19.4 \\
\hline 1996 & 19.7 \\
\hline 2000 & 18.9 \\
\hline 2004 & 18.2 \\
\hline 2008 & 16.8 \\
\hline
\end{array}

Find the equation for the least squares line. Let $x$ correspond to the number of years since 1992 and let $y$ correspond to the average number of pupils per 1 teacher.
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Enter the data into Desmos (desmos.com), You should end up with a screen like the one below. Take special note of the data values in the first column. The $x$ values (in this case called $x_{1}$ ) are described as the number of years since $1992 .$ This means that $1992,1996,2000, \ldots$ corresponds to 0 , $4,8, \ldots$

Examining the screen above, we see that $m=-0.1675$ and $b=19.94$. This means the equation of the least squares line is
$y=-0.1675 x+19.94$

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