Second, you don't need two conditions:

“IF(O12-(O12/100*80)<S12” and “IF(O12-(O12/100*90)<S12”

IF(O12-(O12/100*80)<S1 then it's certanly IF(O12-(O12/100*90)<S12


So what you looking for? To be less than 20% or less than 10%?