How to know what the "average" is of a value? [on hold]

How to know what the "average" is of a value? [on hold]

For example, say you have ten graphemes as follows: 1▒ 2▒
3▒ 4▒ 5▒ 6▒ 7╢ 8╢ 9╢ 10╢
The first six will be called nCa, and the last four will be called nCo.
Between nCa and nCo, what is the average, and why?
Basically, in math, what system constitutes, measures, or determines what
"average" means with different keys, elements, or arrays of data,
constants, or anything?
Bear in mind that I am not good at math beyond arithmetic, for the most part.