Hi Annag88,
Your Question:
Professor taught a few classes the following grade averages for the classes were, 82%, 86%, 91%, 74%, calculate the mean?
Definition:
Mean - "is the average of the numbers: a calculated "central" value of a set of numbers. To calculate it: add up all the numbers, then divide by how many numbers there are."
Solution:

= 333 ÷ 4
= 83.25%
Final Answer:
Mean = 83.25%