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

High School Mean Test Score Number of ninth graders (Frequency)

Glenwood 76 285

Central 90 322

Lincoln 70 187

The city's PR manager, who never took statistics, claimed the mean score of all ninth graders in the city was the average of 76, 90, and 70, which is 78.7. Of course, that is incorrect. What is the mean score for all ninth graders in the city? Round to one decimal place.

Mean of all ninth grader's scores =