How many $$0$$\textquotesingle s does the product of $$1\times 2\times 3\times 4\times 5\times 6\times \cdots \times 25$$ end with? 
Overseas Competition->Knowledge Point->Number Theory Modules->Prime Factorization
There are $$6$$ factors of $$5$$ when you prime factorise~ $$1\times 2\times 3\times 4\times 5\times 6\times \cdots \times 25$$. 