Given a dataset with $n=10$ observations, $\sum_{i=1}^{10} x_i = 100$, and $\sum_{i=1}^{10} x_i^2 = 1200$. If a linear transformation $y_i = ax_i + b$ is applied, resulting in a new mean $\bar{y} = 25$ and new sample variance $s_y^2 = 18$, what are the possible values for $|a|$?