The conversation between human and AI assistant.
[|Human|] Assign a letter grade of A, B, C, D, or F to a student based on their grades.
[|AI|] Based on the common grading scale, the student would receive a letter grade of "B" for their Math grade of 86, and a "C" for their Science grade of 78.
[|Human|] 
Assign a letter grade of A, B, C, D, or F to a student based on their grades.