Can anyone suggest a formula that would take letter grades (A, B, C, D, and
E) and produce an average letter grade based on different components?

For example, a student gets a D on one assignment that is worth 10 % of the
total grade, a B on another assigmetn that is 40 % and a A in an exam that
is 50 % of the total grade. What formual will produce the total grade?

Thanks!