Page popularity is very important for any website to rank well in Google, and Google calculates this popularity in terms of “PageRank”, by giving each webpage a particular rank out of 10. It depends on the number of links coming to your website. This is same as for example if 10 people trust you and points you then Google automatically shows the trust in you.
The PageRank algorithm was built on the basis of the original thesis authored by Sergey Brin and Larry Page while they were undergraduates at Stanford University. In the simplest terms, the paper states that each link to a web page is a vote for that page. Votes do not have equal weight.
Firstly, all pages are given natural but minimum amount of PageRank. Pages can increase their rank by receiving links from other pages, as shown in figure
When a page links to some another page, it passes some amount of PageRank to that page, now this amount is always less than the total of the page’s PageRank.
Matt cutts once described in his blog that a page might pass 85% to 90% of its PageRank.
Page passing its PageRank
If any webpage links to only one other page then it passes all its passable PageRank to that page. Often any page links to more than one page. Hence the passable PageRank will be divided equally in all the linked pages. Internal links within the pages still pass the PageRank through them, so they have value. In fact this scenario becomes more complicated when there exists cross linking between various websites. Since after the introduction of PageRank, the strategy of Google has been varied in many different terms but the basic idea remains the same.