Random Number will not repeat

Hi friends,

I am making a number game please help me :-

I have a MovieClip in the library in that movieclip i have a dynamic text field named “numTxt” and i give class name “Ball” from linkage, now i want create 10 movieClip by addChild method.
i genrate random number in that text feild. and its workning fine.
but some times some numbers are repeating, thats the problum. the numbers should not be repeat.

var myBall:Ball;

for (var i:Number = 0; i<10; i++) {
    myBall = new Ball();
    addChild (myBall);
    myBall.x = i * 100
    myBall.newTxt.text = String(Math.ceil(Math.random()*100))

can anyone help me ???