Its good to have look at challenging query situations every now and again as most Access problems are solved by queries, not code. Doug Steele wrote an article on how to classify student marks into Grades A to F. Have a look and see if you can follow the logic. Even if you can't, if you are a database programmer, you may need to one day.
You will find many challenging articles on queries on the LHS of Doug's article. Read one query article a week and you will be a much better programmer as a result.