private function sum(... nums):Number {
    var total:Number = 0;
 
    for(var i:int = 0; i < nums.length;i++){
        total += nums[i];
    }
 
    return total;
}

http://flexman.info/2008/12/18/example-shows-how-to-use-variable-parameters-in-flex/

Use Variable Parameters In Flex

ActionScript 3