Specific Formula for calculating Average

[Afi83]

Hi there

I want to do something like this in formula field.
I want to calculate average on specific records on my reports. This is for calculating average grades of students.
I want to do like this:
If {course.courseName}(i)={course.courseName}(i+1) then
GradeMax=max{grades.grade}
This code is for incorporating the max marks of each student in each course.

I want to separate the specific grades of each student for other weighting (such as .05):
This is the code I want to do:
If {course.CourseName}="Math" then
Math2=math*0.5
I want to use this number for calculating overall average.

Lastly for calculating the overall average I want to calculate other grades averages and then multiply by these specific numbers:
Average=grademax+math2+otherGrades In recordes/recordsNum

How can I do something like this in Crystal report?

Thanks for any helps