Hi Itamar,
Thank you for your reply and for adding the formulas for 4 questions with 4 options. Inspired by your post and using FLOOR and CEIL, I started playing with 2 categories, 4 questions, 4 options and the feedback #1 to 4-6, feedback #2 to 7-9, feedback #3 to 10-12 and feedback #4 to 13-16. I attached a preset, which should work in Moodle 2.7 and 2.8.
With kind regards,
Hartmut