Change alpha of movieclip on button click

hii, i am developing one small imteractive game.in that i’m getting one difficulty.

Difficulty is: i want to play a moviclip whenever i 'll click on button ,and .For that i hav applied logic in following way.

function onMouseClick(event:MouseEvent):void
{

this.alpha=0;              (alpha of 1st movieclip will 0 )
quack.alpha =1;          (alpha of 2nd movieclip will 1 )(quack is instance name of 2nd movieclip that i need to  call)
 
 }
 
 function onOut(event:MouseEvent):void 
 {        
   quack.alpha = 0; (alpha of 2nd movieclip will 0 )
   this.alpha=1;      (alpha of 1st movieclip will 1 )

 }    

whenever i’am clciking on first movieclip(btn), it definitly goes to 0(i.e off), but 2nd movieclip(instance name “alpha”) is not coming to 1.

is this my logic is correct? what shoud i do to solve this problem?