Quizzes are graded for mastery and the score is based on the total number of possible correct answers. (Some quiz questions are multiple select allowing for more points than the number of total questions in the quiz.)

Progress on quizzes is saved until the student selects "Submit."

So that grades are properly recorded, students should keep in mind that they can only have one  tab open at a time. (If a student opened more than one tab, a grade will only record for the last tab opened.)