sum of 2 radio groups

I have made my first adobe designer form/questionnaire and every thing works fine.

Now I would like to ad some validation to the user input.
the questionnaire have 20 questions and each question have the valor of 5 point/5% and each question have a A/B statement - so if you give 5 points to q1a then q1b most be given 0 points so that the total of q1 equals 5 point/5%.

I would like to do something like:

* on mouse out question x
* sum radio group A+B ≠5
* then pop up with instruction that each question must have the valor of 5 points

I do not know if this is the right way to go or if you could send me in the right direction.

thanks for your time and held
HansPS