select avg(N.number) as Average
from (
	select t.team_name, count(tt.team_id) as 'Number'
	from teams as t
	left join (
		select t.team_id, t.TEAM_NAME
		from teams as t
		join employees as e on e.TEAM_ID= t.TEAM_ID
		where e.gender = 'F'
	) as tt on t.TEAM_ID = tt.team_id
	group by t.team_name
) as N