What is $\cfrac 1n$ in this expression? 
I bought a T-shirt at Kenendy Space Center a while back that had this expression on it:
$$
B > \frac1n\sum_{i=1}^n x_i
$$

And below it is captioned "Be greater than average."
I can see the "Be greater than" and the "average" in the expression, but I do not understand what the $\cfrac 1n$ is for.

So, what is the purpose of $\cfrac 1n$ in the expression above?

(Sorry, I have absolutely no idea how to tag this)

The average (arithmetic mean) is the total of all entries over the number of them.
