Q:

How to left align in the page (not only in the cell) math expressions (written with latex) in markdown?

Today, I'm able to left align mathematical expressions with markdown and latex :  
$$
\begin{aligned}
& P(X = r) = \frac{1}{n} \\
& P(X \le r) = F(X) = \frac{r}{n} \\
& E(X) = \frac{n+1}{2} \\
& V(X) = \frac{n^2 - 1}{12}
\end{aligned}$$

or 
\begin{align}
& P(X = r) = \frac{1}{n} \\
& P(X \le r) = F(X) = \frac{r}{n} \\
& E(X) = \frac{n+1}{2} \\
& V(X) = \frac{n^2 - 1}{12}
\end{align}

All the expressions are then left aligned, but they are still put at the center of the page :  
I show you how to have 114 :
                         114 = 112 + 2
                         114 = 100 + 7 + 7
                         114 = 50 + 50 + 7 + 3 + 4

(by default latex does this formatting if you don't align :
I show you how to have 114 :
                              114 = 112 + 2
                            114 = 100 + 7 + 7
                        114 = 50 + 50 + 7 + 3 + 4

)
I do not want reader eyes having to go left to start reading an explanatory sentence, then at the center of the page to read a formula, then left again for the next sentence, and so on.
I would like my mathematical expressions to be also left aligned on the page. And have this :
I show you how to have 114 :
114 = 112 + 2
114 = 100 + 7 + 7
114 = 50 + 50 + 7 + 3 + 4

I do not want to use single $ delimiters, $ ... $ because they degrade mathematical formulas making them less readable.  
Any summation depicts the differences : $$s^2 = \frac{1}{n-1}\sum_{i=1}^{n}(x_i - \bar{x})^2$$ and $s^2 = \frac{1}{n-1}\sum_{i=1}^{n}(x_i - \bar{x})^2$ don't display the things with the same quality : in inline mode, latex "compress" in height all the elements the most it can to avoid making the line higher than it is.

A:

Thanks to Alain, his solution works. Add to the metadata section of the markdown file the classoption: fleqn. Don't add the \usepackage{amsmath} with pandoc : it might cause a conflict. Only the classoption.
---
classoption: fleqn

title: "Statistiques et Spark"
author: Marc Le Bihan
geometry: margin=2cm
urlcolor: blue
---

$$
\begin{aligned}
& P(X = r) = \frac{1}{n} \\
& P(X \le r) = F(X) = \frac{r}{n} \\
& E(X) = \frac{n+1}{2} \\
& V(X) = \frac{n^2 - 1}{12}
\end{aligned}
$$

then works, or this alternative syntax can be used :
$$P(X = r) = \frac{1}{n}$$
$$P(X \le r) = F(X) = \frac{r}{n}$$
$$E(X) = \frac{n+1}{2}$$
$$V(X) = \frac{n^2 - 1}{12}$$

that adds a subtle spacing in between lines, who might please or not.

