I Got an A!
America is famous for doing things differently or sometimes backward. Most schools in the world use standard numbers or percentages for the grading system, in both school and college. In America, they created their own system which is based on letter grades. The highest or best grade that you can get is an A+ and the lowest grade is an F-.
Not only have Americans decided to change the grading system to letters instead of standard numbers, which can be very confusing to non-Americans, but they decided to take it one step further. Adding a plus sign or minus sign next to the letters as seen in the reference above doesn’t really make sense to most people but that is just the way grading is commonly done in America.