if 20 low pr links point to my site with xx keywords. and 3 high pr links point to my site with the same anchor as kewords.the other is the same.(same theme, same total links in a site) my question is.if low pr links contribute to my site pr as xx times as to high pr site, do low pr sites contribute to my site relevancy for xx keyword as times as high pr site? other question:low pr sites make my site position in serp for xx keyword higher than high pr site or lower than?
The main thing is that the sites need to be on topic. It's wise to have the anchor text vary a bit between links. It's also important to not have only low pr links to your site. Try and get a few quality links in there (three sounds good) - preferably from quality sites in your niche. It's not about having one or the other. Once your site starts ranking, you will get low quality sites linking to you. Spam sites, to be exact. This won't hurt your rankings, but don't spend too much time hunting low quality links.