<Li> E = zero grade points per semester hour </Li> <Li> EN = zero grade points per semester hour </Li> <P> Students' scholastic standing or grade point average is obtained by dividing the total number of grade points earned by the total number of semester hours attempted for which the foregoing grades have been assigned . Grades of "I," "W," "NR," and "X" are not used in the computation of grade point average . Grades earned in college preparatory classes do not count in the computation of the grade point average . </P>

What do the grades a b c d and f stand for