John is a gardener. The other day he bought a stack of posts and decided to put them around his garden. He planted the posts 2 feet apart and found that he needed 200 extra posts. Annoyed, he pulled up his posts and replaced them, but this time placing them 3 feet apart. Now he had 25 posts over. How many posts did he buy?
As ever, please do NOT post your answers, but do feel free to say whether you think you solved it and how long it took. Solution on Monday.