My understanding is that PageRank works only on a per page basis (which seems obvious enough). But The reason I asked the question in the title is that I noticed that yahoo answers results tend to rank high in google when the pages themselves are not really well optimized and when i've checked the PR of a few pages they usually have none. So what's going on here? Sorry if it's something obvious but I just don't understand how this could be according to what i've read. yahoo.com and even answers.yahoo.com each have very high PR, but then that is at the site level and not the actual level of the page(s).
If your domain has PR 8 and links to 3-4 others pages within your site, all of them will also get good PR automatically.
Ranking good in search results got nothing to do with PR. It all depends on the backlinks of that particular page have. Obviously, in this case, yahoo answer have a lot of backlinks that pushed it to top search results.