Question 144709
Your solution is spot on.  However, if you had more details about the scoring of the test, you might be able to adjust your interval somewhat.  For instance, if you knew that the maximum score on the final was 100, then you could adjust the upper limit to 100] and resign yourself to the fact that an A isn't in the cards.  If you knew that the scoring system never results in fractional parts of points, you could adjust the lower limit to the next higher integer, and the upper limit to the next lower integer.  Or perhaps the final will consist of 20 questions, each worth 5 points, and no partial credit given.  In this case the lower limit could be written either (75 or [80.