What exactly do you mean by not working? Is it throwing an error message or are you not getting the result you were expecting? I'm guessing it's the latter, this would be caused by order of operations.
Add some parenthesis around your criteria:
The first example I showed you should be effective.
It's a simple order of operations rule. Multiplication and division will always be executed before addition, therefore, the reason you are not getting the value you expect is because access is preforming all of the multiplication and division, THEN the addition. By adding the paranthesis, you are explicitly telling access that you would like to add the first three values, THEN do the division. Try it out.