See the documentation for

Expression Manager and the

HowTo examples.

Although you could create a single expression that has all 100 variables, I'd recommend breaking it up. So, since you have 10 categories, you could create a hidden Equation question for each category to create the category-specific score. Say your variables names are named by category (A-J) and question within category (1-3) - so A1-A3, B1-B3, ... J1-J3. Then, scale-scores would be like this (where let's call the category score Xscore where X is the category.). So Ascore would be:

sum(A1.NAOK,A2.NAOK,A3.NAOK)

Then, the total score would be the sum of each of the category scores (plus your starting score of 50).

sum(50,Ascore.NAOK,Bscore.NAOK,...,Jscore.NAOK)

For your reports, you could show the final score (let's call it finalScore) as

Thanks for filling out our survey, {TOKEN:FIRSTNAME}. Your final score was {finalScore}.

Incidentally, the reason for all the NAOK is in case you have conditions on your questions - the NAOK would let you compute the scores anyway. If conditions hid any of the parts of the sum and you didn't use .NAOK, then {finalScore} would always = 0.