Partial points in quizzes - is there any way of awarding partial points (half points etc)?

Hello,

I have a quiz with a question that requires participants to select a number of fields on a screenshot of some software. There are 21 fields on the screenshot, only 8 of which are right answers.

If the user correctly identifies all eight fields, I want them to score 1 point (it's a relatively easy question and I don't want them to get a disproportionately high score). However, I still want them to get credit (pro rata) if they only select some of them (selecting 7 of them would score 0.875 for example).

Since Captivate doesn't appear to allow for decimal values to be assigned as point scores, the obvious solution is to scale up my scores throughout the quiz to ensure the right weightings are applied.

The problem is this: if the user selects ANY incorrect fields, I want them to score zero for the question (so 6 right answers and 2 wrong ones would score 0, 8 right answers and 1 wrong one would score 0, and so on).

I can't use penalty points, because we'd need to know how many correct answers were selected to deduct the right amount and I don't want to facilitate potential negative scores.

I can easily use variables and advanced actions to establish a final score, but I understand it's not possible to manually substitute the system variable that holds the points scored with that value?

Am I asking the impossible?