Configurable chances for events

Already got the base idea down, I don't really want to share the code unless I completely have too, because once I'm done I'm gonna throw it on the website. I already got this 100% working, until I realized the percentage system I was using isn't actually accurate.
@timtower (I know you're an amazing developer, just came to mind)
I'll give you a snippet of what I was doing:

Code:

Random r = new Random();
                      int  n = r.nextInt(100) + 1;
                      if (n<= emerald) {
                          blocktobe = Material.EMERALD_ORE;
                      }
                      else if (n<= diamond) {
                          blocktobe = Material.DIAMOND_ORE;
                      }
                      else if (n<= gold) {
                          blocktobe = Material.GOLD_ORE;
                      }
                      else if (n<= iron) {
                          blocktobe = Material.IRON_ORE;
                      }
                      else if (n<= redstone) {
                          blocktobe = Material.IRON_ORE;
                      }
                      else if (n<= lapis) {
                          blocktobe = Material.LAPIS_ORE;
                      }
                      else if (n<= coal) {
                          blocktobe = Material.COAL_ORE;
                      }
                      else if (n<= stone) {
                          blocktobe = Material.STONE;
                      }
                      else {
                          blocktobe = Material.COBBLESTONE;
                      }
                      b.setType(blocktobe);

This, obviously.. doesn't really work percentages. (The "emerald", "diamond" and so on are values inside of the config file)
Is there a better method for actually calculating proper percentages off of a configuration file input?
I can throw in the configuration right here, too.

Code:

emerald: 3
diamond: 3
gold: 15
iron: 20
redstone: 25
lapis: 30
coal: 35
stone: 40

I'm not the type you gotta spoonfeed, I just need an idea to build off. I thought this would work, but it doesn't work quite right haha

 

@u_mad_bros
This might give you an idea:
https://bukkit.org/threads/drop-percent-chance-help.100876/

 

I read it, and someone said "just add this".. that doesn't explain why. At all.
EDIT:
Doesn't really work the same, either. That only works for a single chance, but I have more than one item. Any suggestions?