I posted this question with the title of Average If which was a misleading
title.

I have a column of invoice numbers and multiple rows of data pertaining to
each one. So one invoice number could have 10 rows of data pertaining to it
so the invoice number will be repeated 10 times. Then on each line is the
time it took to receive the data so this number will be the same on all 10
lines. I have hundreds of rows of data but only a handful of invoice
numbers. I need to find the average of the days based on the unique count of
the invoice numbers. I already have my formula for the unique count but now
need one for the average when the invoice numbers are not in contiguous cells
down the column.

Example:
Col A Col B
Invoice # # Days
12345 11
12345 11
12345 11
98995 15
66438 37
12345 11
98995 15
12345 11

So there are 3 unique invoice numbers. How do I write the formula to find
the average number days it took to receive all three? I'm in Excel 2003.