There are 35 students in a class, and they all like at least one of the two fruits, apples and bananas. The number of students who like apples is three times the number of students who like both, and the number of students who like bananas is five times the number of students who like both. How many students like both? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle->Inclusion-Exclusion Principle for Two Sets