I have,
A B
1 5/1/2005
2 5/2/2005
3 5/3/2005
4 6/1/2005
5 6/2/2005
6 6/3/2005
7 7/1/2005
8 7/2/2005
9 7/3/2005
10 7/4/2005

I want the Average of the different months, May for example, why this:

=SUMPRODUCT(SUBTOTAL(1,A1:A10)*(MONTH(B1:B10)=5)*( YEAR(B1:B10)=2005))

is giving me 16.5 ?

TXS