Flash As3 random selected Disks plus Chance/luck - actionscript-3

Question

My question is how can i add chances to the random selected disks in Actionscript3.0.
SO if the player presses the disks button he/she gets 30% chance to roll disk7 and 40% on disk6. How can i pull this trough.
disks.addEventListener(MouseEvent.MOUSE_DOWN, hitDisk);
function hitDisk(event:MouseEvent):void{
disks.gotoAndStop(Math.ceil(Math.random()*7));
}
Disks[movieclip] > haves 7 keyframes with disks inside of it.
The final frame is the special disk. Every disk haves a instance name.
Disks[movieclip] > (frame1)diskOne, (frame2)diskTwo, (frame3)diskThree.....and so on.
(disks are just like dices but round shaped)
Some help would be nice!!! Thanks!!!

Answer 1

I think you want something like this:
function hitDisk(event:MouseEvent):void{
var rand:int = Math.random() * 100; //gives you a number between 0 and 100
if (rand <= 40) //40% chance
disks.gotoAndStop(7);
} else if (rand > 40 && rand <= 70) { //30% chance
disk.gotoAndStop(6);
} else { //30 % chance
disk.gotoAndStop(5);
}

Answer 2

If you search up ‘random number generators with a bias’ or ‘adding a bias to a random number generator’ (something along these lines) you should find ways to do what you want: to have certain numbers in your random number ‘rolling’ algorithm produce certain numbers more then others.
I’m going to make an assumption here that a disc is like a die, but with seven possible outcomes.
This is one basic method I've used in the past for a similar problem.
You mentioned:
30% chance to roll 7
40% chance to roll 6
I’m going to assume then that 1,2,3,4,5 have an equal chance in the missing 30% chance, so 30% divided by 5 is 6% chance for all the other numbers. So:
30% chance to roll 7
40% chance to roll 6
6% chance to roll 5
6% chance to roll 4
6% chance to roll 3
6% chance to roll 2
6% chance to roll 1
So given these percentages (totaling 100%), you could make an array with 100 spaces and:
fill the first 6 indexes with ‘1’
fill the next 6 indexes with ‘2’
fill the next 6 indexes with ‘3’
fill the next 6 indexes with ‘4’
fill the next 6 indexes with ‘5’
fill the next 40 indexes with ‘6’
fill the next 30 indexes with ‘7’
Then use Math.random() to choose an index at random from this array. Since there are 40 chances out of 100 for ‘6’ to be picked, ‘6’ would come out 40% of the time. And so on with the other numbers.
This can be pretty wasteful to have a large array just for this, but you can improve this with some math (right away I can see that the array can actually be half the size and still contain the desired percentages, just by dividing everything by 2). Or you could take advantage of the fact that numbers 1,2,3,4,5 have an equal outcome and separate it out resulting in an even smaller array (just to calculate the biased outcomes), and so forth.