Good article on a study from AHRefs to show the relationship between ranking pages, and how they rank for other keywords...
Ahref has published an interesting study that shows how many other keywords a single page can rank for in Google. Typically, SEOs tend to try to optimize each individual page for its own keyword phrase. But the study showed that the average number one ranking page will also rank in the top 10 results for about 1,000 other relevant keywords. The median value is less than half that, with around 400 relevant keywords.
http://searchengineland.com/ahrefs-keyword-ranking-study-274779
