I have 2 cells which I select entries from a drop-down (A1 and A2) B2 then
does a simple subtraction of whats selected in A1 and A2

A user can select only A1 or A2, this would be incomplete thus I want in
this instance to "blank" out the value returned in B2 i.e. with white font,
as the result is not very meaning full

How would I do this under conditional formatting in B2

I thought of something like this if(or(A1=" ",A2=" "), but don't think you
can use "IF" in conditional formatting


Thanks