Counting Check Boxes with values

I have a sub-form where I gave each check box a value: sum(ICB6, ICB7, ICB11, ICB12, ICB16, ICB17, ICB21, ICB22), but what I want to do now is take this total and divide by the # of check boxes actaully checked. For example; if 2 of the boxes are checked my total is 7, then I want to divide it by 2 (the number of boxes checked) to get 3.5 as my score. I can not figure out how to make that happen?