An average for numbers that fall within a criteria

[bzax33]

I need to figure out a way to get an average for the numbers in column A, but ONLY those numbers in column A that have the number "1" in column B.
example:
Column A Column B
3 5
6 1
4 1

The average would be "5", because the numbers 6 and 4 have "1" next to them in column B.
Thanks!

 

[barry houdini]

You can use AVERAGEIF in Excel 2007 and later, i.e.

=AVERAGEIF(B:B,1,A:A)