I get this question a lot at the end of the year. Here's help. You have to score an 85% for the year to exempt your exam. In order to figure out what you need to make Q4 to average an 85%, follow these instructions.
Exam Exemption Formulas (This should work for all year-long courses.)
Know your averages for S1 and Q3. (S1 = _____; Q3 = _____)
You have to make a minimum of an 85 to exempt for the year, so your first equation will be finding the total points of an 85 average for each semester: 85 + 85 = 170
Now, solve for Q4: take the total points necessary for an 85, and subtract your S1 average: 170 - S1 = S2
Now, solve for S2: (Q3 + Q4) / 2 = S2
Example
Hypothetical averages for S1 and Q3. (S1 = 78; Q3 = 90)
You have to make a minimum of an 85 to exempt for the year, so your first equation will be finding the total points of an 85 average for each semester: 85 + 85 = 170
Now, solve for S2: take the total points necessary for an 85, and subtract your S1 average: 170 - 78 = 92
Now, solve for Q4: (90 + Q4) / 2 = 92
90 + Q4 = 184
Q4 = 184 - 90
Q4 = 94
In order to exempt the exam with a year average of an 85%, this student would need to make a 94% for Q4.