how to reset variable in javascript

this is the code

var x = Math.floor( Math.random() * 10 );
setInterval(function () {

    if (x >= 5) {
          $('.test').show();
          setTimeout(function () {
                         $('.test').hide();
                 }, 2000);
    } else {
        x = Math.floor( Math.random() * 25 );
    }

}, x * 1000);

this code show .test with the same random like if the x=8 it will stay 8 and doesn't change what I really want is changing x to another number

I've tried to put var x in the local scope and it show me x in setInterval is undifined

I wanna $('.test') shows in a random way between 5 and 10 second like first time show after 7S, second time after 9 second, etc... .