How many whole numbers between $$1$$ and $$500$$ are divisible by $$6$$ but are not divisible by $$8$$? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle->Inclusion-Exclusion Principle for Two Sets
Every $$6$$th number $$\left( 83 \right.$$ of them$$\left. {} \right)$$ is divisible by $$6$$. Every $$24$$th number $$\left( 20 \right.$$ of them$$\left. {} \right)$$ is divisible by $$6$$ and $$8$$, and $$83-20 = 63$$. 