In a city with three high schools, all the ninth graders took a Standardized Test, with these results:

High School	Mean score on test	Number of ninth graders
Glenwood	78	286
Central City	95	322
Lincoln High	70	168

The city's PR manager, who never took statistics, claimed the mean score of all ninth graders in the city was 81 . Of course, that is incorrect.

What is the mean score for all ninth graders in the city? 

Mean of all ninth grader's scores = Round to 2 places