A finite set, possibly.
No set number.
If the set has n elements, the number of subsets (the power set) has 2n members.
The mean is the average; the total of the members of the set divided by the number of members n the set.
It is a one-to-one correspondence and it is defined as situation which occurs when the members of one set can be evenly matched with the members of a second set.
That's the average value of all the members of the set.
That's the average value of all the members of the set.
The objects within a number set can be caled as "Elements" or "members".
If it weren't considered a set, lots of rules would need exceptions for the case there are no members in a set.
A set with 27 members has 2^27 = 134217728 subsets - including itself and the null set.
This is the Arithmetic Mean (also known as the average).
Secondary consumers
The Reapportionment Act of 1929