This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Your English is difficult to understand (perhaps you could get someone who speaks better English to write your post) but I think you are asking how to find the average grade of a group of students. An instance of StudentV2 represents *one* student, so I don't think it makes sense for such an object to know the average of four students. You could define a class, say StudentCohort, that holds a collection of students. If you ask a cohort for its average, it will find that out by asking each individual for its grade, then doing the math.