If either column A has "yes" or column B has "yes", column C should show
"yes" too but if BOTH columns "A" or "B" have "N/A" "C" should say "N/A",

A B C
Yes no yes
No Yes Yes
Yes Yes Yes
No no No
N/A N/A N/A

I tried =IF(OR(a1="Yes",b1="Yes"),"Yes","No")
it is giving me

A B C
Yes no yes
No Yes Yes
Yes Yes Yes
No no No
N/A N/A no

C5 is the thing I want to change from "no" to "NA"