Suppose that,
- the average person has $2$ $1/2$ children.
- only whole children exist
It should be straightforward to notate:
- If an average person exists, then that person has two $1/2$ children
- there does not exist $1/2$ a child
- Therefore, the average person does not exist.
However, I can't figure out to notate the $1/2$ child part so that the meaning of $1/2$ is clear. The problem, as I see it is that if whole children exist $(1/1)$ then half children exist $(1/2 + 1/2)$.
How do I convey the idea in notation?
I would say it like this: "Statistically a person has on average a half child." It is different from your wording. An average person cannot have a half child.
Mathematical formulation:
$x_i:$Number of children of person i
$x_i \in \mathbb N$
$\overline x:$ Average number of children per person.