What is the ones digit of the product $$80\times 70\times 60\times 50\times 40\times 30\times 20\times 10\times 5\times 2$$? 
Overseas Competition->Knowledge Point->Number Theory Modules->Division without Remainders->Applying the Properties of Dividing without Remainders->Maximum/Minimum Problems of Division without Remainders 
Since $$10$$ is a factor of this product, the ones digit is $$0$$. 