While reviewing MDL-50894 I noticed that the method used to compute the percentage of the grades was not right in the availability condition grade.

In get_cached_grade_score a few things are wrong:

1. Assumption that min and max have different values, this is not the case in single item scales.
2. Using grade_grade.rawgrademin/max, that is not reliable see MDL-46618
3. Duplicates the code that generates the percentage (grade_format_gradevalue_percentage), which can be a problem as not everyone would assume that in the following example the percentage is 50%, and we might change that later:
   • grademin = 50
   • grademax = 100
   • finalgrade = 75

The third point is the least important but it's good to consider it.