$$150$$ students went to a $$\text{CCA}$$ fair and all of them at least tried out one activity. $$85$$ students tried out Sports activity. $$77$$ students tried out Art activity. How many students tried out both Sport activity and Art activities? 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
$$85+77-150=12$$ 