sum of two variables: whats the formula

Thanx for the formula.....

[James]I had figured out the same solution as you did. But like always one solution leads to another problem :-)

What I want to make is a survey which at the end will lead to a 'comment'. So each answer has a another value (like 5, 0,-2, -5). The total of all the answers leads to a comment at the end of the complete survey , like' you did not/ well on this subject' (memo_end).

Adding memo1 and memo2 is not safe for the final result of the test/ suvey, because the student can click several times in the same question (ie when he makes a mistake or wants to change his first choice) and so every time he adds the value behind the click (answer) to the totall. So the endresult is not reliable. I tried to repair that by not adding but setting the value, so only the last click will be setting the var (memo1 or 2 etc). But at the end of the suvey there has to be a sum (add) to get a totall (memo 1+memo2+ etc) in memo_end. Unfortunatly memo_end 'remembers' (adds) all the clicks of the student in the question (setting the value). I can't figure out how to stop the adding in memo_end during the survey and letting it count only the last setting of the values. 

Now I'm trying to make the survey as a Test (because a Test will block all the clicks and will only 'add' the last click to the testtotall), in which I will make every answer as an individual Question (with a value) but you can't give a question (in a test) a negative value, so.....

Well I hope you can understand my problem :-) and perhaps can give me a hint ...