Help with functions?

okay so this is my code for my game that counts up the score every time you click on each positive button, but counts down when you click on the negative buttons.

what i would like to do is to show the POSITIVE button at random instead of using the time line to show the positive scoring button in different places on the stage.

i thought maybe making some more positive buttons, making them not visible then running a new function, so one of the positive buttons would show when one function is called at random?

var score: Number;

    //event listeners to increase the score when specific event when cued

    btnPos1.addEventListener(MouseEvent.CLICK, on_press);

    //event listeners to decrease the score when specific event when cued

    btnNeg1.addEventListener(MouseEvent.CLICK, on_press2);

    btnNeg2.addEventListener(MouseEvent.CLICK, on_press2);

    btnNeg3.addEventListener(MouseEvent.CLICK, on_press2);

    btnNeg4.addEventListener(MouseEvent.CLICK, on_press2);

    //sets the score to 0

    function init():void

    {

        score = 0;

           scoreWindow.text = score.toString();

    }

     //updates the score

    //removes all positive scoring buttons     as only one can be pressed at a time

    function on_press(event:MouseEvent):void

    {

        updateScore();

        btnPos1.visible = false

    }

     //increases the score by 5

    function updateScore():void

    {

        score += 5;

         scoreWindow.text = score.toString();

    }

     //updates the score

     function on_press2(event:MouseEvent):void

    {

        updateScore2();

    }

     //decreases the score by 10

     function updateScore2():void

    {

        score -= 10;

         scoreWindow.text = score.toString();

    }

    init();