Weighted mean Example

This is the example i found for weighted mean !!!!!!

A teacher might say the test average is 60% of the grade, quiz average is 30% of the grade, and a project is 10% of the grade. Suppose Mary got 90 and 78 on the tests; 100, 100 and 85 on the quizzes; and an 81 on the project. Her course grade would be:
Test average = (90 + 78)/ 2 = 84
Quiz average = (100 + 100 + 85)/3 = 95
Course grade = .60*84 + .30*95 + .10*81 = 87