I can only recommend taking a look at the statistics section of khanacademy.org for how to do the math. There is a section on how to work out just this sort of scenario, and I can't remember how to do it offhand. I've sworn off statistics.:noway:
An option that will give you an idea of what those combinations can look like is to color a few out on graph paper to find then develop a visually appealing block arrangement.