MathJax has some font size issues with MathML. For now, I recommend using it with TeX. TeX mode automatically centers output, have a look at the source of this page to see how to turn it off.
\[ Avg(X) = \frac{1}{|X|} {\cdot} \sum_{i=1}^{|X|} x_i \]
\[ Avg(X) = \frac{1}{|X|} {\cdot} \sum_{i=1}^{|X|} x_i \]
\[ \frac{d}{dx}\frac{f(x)}{g(x)} = \frac{f'(x){\cdot}g(x) - f(x){\cdot}g'(x)}{g(x)^2} \]
\[ \frac{d}{dx}\frac{f(x)}{g(x)} = \frac{f'(x){\cdot}g(x) - f(x){\cdot}g'(x)}{g(x)^2} \]
\[ \frac{d}{dx} f(x)g(x) = f'(x){\cdot}g(x) + f(x){\cdot}g'(x) \]
\[ \frac{d}{dx} f(x)g(x) = f'(x){\cdot}g(x) + f(x){\cdot}g'(x) \]
\[ \int_{a}^{b} {u} {dv} = u{\cdot}v - \int_{a}^{b} v du \]
\[ \int_{a}^{b} {u} {dv} = u{\cdot}v - \int_{a}^{b} v du \]