Using the Formula field, is there a way to calculate how many check boxes are checked?

Here is an example. I have 3 check boxes: check1 (if this is checked, the value is 10), check2 (if this is checked, the value is 20), check3 (if this is checked, the value is 30) and a formula field: formula1.

In the formula field, I want to test how many of those 3 checkboxes are checked, and add the value for each checkbox.

So if check1 is checked, then formula1 = 10; if check2 is checked then formula1 = 20 and so on. But if check1 and check2 is selected, then formula1 = 30.

The only way I could think of is by creating a variable and adding to it for the value of formula1. Does anyone know another way using a combination of functions?

Thanks,
Daniel