I'm having difficulty figuring out how to set my gradebook up to average a test and retest.  In our class students must pass each test with a 75%.  If they fail to obtain a 75% on first test they take a retest and the average of the two tests must be 75% to continue in the class.  So not every student will have a grade for the retest. How do I set this up.

Thanks, I hope I was clear enough for you to understand.