In a List

I receive Lists of uncertain size, usually between 4~10 counts long:

{Apples, Orange, Pear, ?, ? ...}  

How can I have Apples have the highest % chance spawning, then orange, then pear?

The effect is essentially the same as picking a random item from a List that looks like this:

{Apples, Apples, Apples, Apples, Orange, Orange, Pear}

If the List size were fixed, I would've done

1. Generate a float between 0.0~1.0;
2. If <0.4, generate Apples. else if <0.2