Random Level Generator

I added a random level generator to the game. It generates 12 blocks between 120 and 480 on the x axis and between 60 and 330 on the y axis. The code is as below...

for (var  i = 0; i < 12;  i++)
{
    var x = Math.floor((Math.random()*10)+3) *40;
    var y = Math.floor((Math.random()*9)+2) *30;

    rects.push(rect(x, y, 20, 20));
}

The first 8 levels are randomly generated then the last 2 are pre generated.