The subject probably doesn't quite call it what it's supposed to be called but, anyway, here's the problem:
Just for the sake of argument, say there are 5 possibilities (each "possibility" represents someone's blog feed for instance.) Over the course of time, each feed receives votes on how interesting it is to the audience reading the feeds.
So, feed1 has received 41 votes, feed2 - 25, feed3 - 14, feed4 - 10, feed5 -8.
What would be the formula for randomly choosing one of the five feeds, while at the same time giving the feeds with a higher number of votes, a better chance at getting selected? In other words, how to randomly choose one of the feeds while factoring in their popularity (or unpopularity, as the case may be.)