Call Function Sequence Randomly

My code is below. I'm simply trying to make the functions random, instead of sequential, Please help, as this is urgent!

/* Start from panel 1 */
_root.show1();
 
var fnArray = [show1, show2, show3, show4];
var counter = 0;
var intervalId;
function callfunctions() {
        fnArray[counter]();
        counter = counter+1<fnArray.length ? counter+1 : 0;
 
}
 
 
function startTimer(num) {
        clearInterval(intervalId); /* Cleared interval, because clicking each button would offset the timer */
        counter = num; /* Removed "-1" because of odd jump */
        intervalId = setInterval(callfunctions, 5500);
}
 
/* Also removed stopTimer(); because we're calling startTimer(); in each button */
 
_root.startTimer(1); /* Starts the timer for panel 1 */

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