Modify sum average formula for weeks (instead of months)

[collegeitdept]

Thank you to Barry for your formula! It worked.

One last question about the sumproduct average formula for months - how can this be modified for weekly averages?

=SUM(IF(FREQUENCY(IF((ROUNDUP(MONTH($A$2:$A$100)/3,0)=MID(AG$4,2,1)+0)*(YEAR($A$2:$A$100)=VALUE(RIGHT(AG$4,4)))*($C$2:$C$100=AG$5),MONTH($A$2:$A$100)),{1,2,3,4,5,6,7,8,9 ,10,11,12}),1))


Weekly data file:

https://dl.dropboxusercontent.com/u/15717201/Excel Question - quarterly average.xlsx


Thanks!