Answer:
(3,16)
Step-by-step explanation:
The degrees of freedom of the critical value F are (k-1,n-k).
We are given that there are four sample group, so,
k=4.
Also, we are given that the each four groups contains five observations, so,
n=4*5
n=20
The critical value F has degree of freedom
(k-1,n-k)
(4-1,20-4)
(3,16).
Thus, the degrees of freedom for the critical value of F are (3,16).