The population of Northtown on January 1 for the years 2001 through 2007 is shown in the table below. What is the average yearly change in population from January 1, 2003, to January 1, 2005 ?

$$\begin{array}{|c|c|} \hline \text{Year} & \text{Population} \\ \hline 2001 & 1{,}506 \\ 2002 & 1{,}612 \\ 2003 & 1{,}726 \\ 2004 & 1{,}844 \\ 2005 & 1{,}972 \\ 2006 & 2{,}098 \\ 2007 & 2{,}224 \\ \hline \end{array}$$

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Find the difference between each year from 2003 to 2005, then average it:

$$\begin{array}{|c|c|r|} \hline \text{Year} & \text{Population} & \text{Difference}\\ \hline 2001 & 1{,}506 \\ 2002 & 1{,}612 & \\ 2003 & 1{,}726 & \\ 2004 & 1{,}844 & 118\\ 2005 & 1{,}972 & 128\\ 2006 & 2{,}098 & \\ 2007 & 2{,}224 & \\ \hline \end{array}$$ $$\text{average} = \frac{118+128}{2}$$ $$= \frac{246}{2} = \boxed{123}$$