In Tim\textquotesingle s class, there are $$20$$ students who can swim, $$25$$ students who can play basketball, and $$10$$ students who can do both. If everyone in the class plays at least one sport, how many students are there in Tim\textquotesingle s class?~\uline{~~~~~~~~~~}~. 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
$$20+25-10=35$$. 