Average of each 25% of column

Bumping an old topic, cause I have the some problem.
How do I calculate the second 25%, the third 25% and last 25% of an range in a column?
With some trial and error I came to this:

second 25%:
AVERAGE(OFFSET(A1,INT(COUNT(A1:A10000)/4),0,INT(COUNT(A1:A10000)/4),1))

third 25%:
AVERAGE(OFFSET(A1,INT(COUNT(A1:A10000)/2),0,INT(COUNT(A1:A10000)/4),1))

last 25%:
dont have yet

Is any of this good?
Can someone plz show me the correct formulas?
Perhaps also the formulas for first, second, third, fourth and last 20% of an range?