Random with probability

I have an array of several objects. I need a function that would pull out one of these things at random, BUT one float variable inside these objects needs to affect the probability of choosing this one object. So if variable in one object is set to 100, and others are 0, it needs to be result of the roll in 80% of rolls (for instance).

So I cast to objects in the array and extract the values of variables from them in a ForEachLoop sequence. Where do I go from here?