Dispatch from percentage

Hi guys,

I'm looking to find a way to randomly extrude a series of objects, so that the total number of objects extrudes it based on a percentage. In the example here, I have ten rectangles and I would like to be able to set a percentage so that there are, for example, always 4 of ten extruded at one height and 6 fo 10 at another. i want to be able to change the random seed so that the configuration shifts.

I am having trouble with the random function here, as it changes the percentage number on the dispatc. Is there another way of acheiving this?