An average uses every bucket, not only the most common outcome. The numerator multiplies each bucket value by how many microstates have that value, then the total is divided by the number of microstates. The result is exact for this balanced toy list; it should not be read as a measured population average without sampling and uncertainty notes.
A statistical average is a weighted count ledger. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The average uses every bucket count
The numerator multiplies each heads count by its multiplicity.