Excel formula help

[reefoid]

I have a spreadsheet with three columns that contain ID numbers. I need to identify how many ID numbers that appear in column A also appear in column C but DO NOT appear in column B.

I'm struggling to work out how to do this. Could anyone advise on what kind of formula I should use to do this? I'm normally pretty good at working these things out so if someone could give me a gentle push in the right direction it would be appreciated.

Thanks.

 

[A[L]C]

are the ids unique?

could do a vlookup in a hidden column for each, then an if in the last

 

[MeMeMeMe]

Maybe something like: Add a 4th column, in it add an expression like:
=IF(AND(ISERROR(Match(A1,B:B,0)),NOT(ISERROR(Match(A1,C:C,0)))),TRUE,FALSE)
Then wherever it shows True, the ID number in column A matches your rules.