Matrix averages

[Guest]

My Dearest Wizards,

Col A is the dates of the year from 1/1 to 12/31
Col B is the initials of my 11 randomly scheduled salespeople ab,bc,cd,de,ef
etc.
Col C is the revenue each brought in for the day.

What formula do I use to find the average daily revenue for salesperson de ?

Thanks for your help with this!
Sam

 

[Tom Ogilvy]

=Sumif(B:B,M1,C:C)/Countif(B:B,M1)

Where M1 contains de