On Mar 30, 1:05*pm, Mike wrote:
I want the sum of C values for each value of (A and B).
For example, A=1, B=a3, then C=11+13+14=38.

Depends on what version of Excel you have.

For XL2007 and later:

=SUMIFS(C1:C100,A1:A100,1,B1:B100,"a3")

For XL2003 and earlier:

=SUMPRODUCT((A1:A100=1)*(B1:B100="a3"),C1:C100)