How do you factor #p^3r^5-p^2r#?
To see what you can factor out, find what is common in both terms. Both terms have p and r, but the maximum number that they share can be factored out.
when you remove two p's from the first term, there is one p left.
when you remove one r from the first term, there are four r's left.
when you remove two p's and one r from the second term, there is nothing left. However, you must put 1 there as a place holder (not 0, because when you distribute anything multiplied by 0 is 0).
So the answer is