I have a column of test scores - N9:N154.

Scores can be grouped into low (<=79), average (80<=x=120), and high
(=121).

I want to have one formula for each group that will find the average score
for that group.

The logic is something like:
Low group: find the average of all the scores that are less than or equal to
79 within N9:N154.
Middle group: find the average of all the scores between 80 and 120 within
N9:N154.
High group: find the average of all the scores higher than or equal to 121
within N9:N154.