Answer:
(n-1)a
Step-by-step explanation:
In this question we have a single factor with number of levels equal to a.
Then the Number of observations that are within each factor setting is equal to n.
So the total number of observations = na.
We have the degrees of freedom for SS(Error) = n - k,
Now, n is the total number of observations,
While,
k is the number of levels of the single factor.
Therefore the degrees of freedom is = na - a
= (n - 1)a.