Top 10% in Excel Sheet

I am working on an excel sheet which has "N" number of records (Columns - Name, Marks).

I need to assign the top 10% of these to a particular category. I know how I can do it manually. (Sort descending on Marks, find the 10% of the total no. of records and add them to a category)

Is there some way I can do it automatically. If someone can help me with the logic, I may be able to develop a macro.