mathematics: - the agd of some student in a university are as follows:20,15,18,21,22,23,23,16,18,19,23,21,19,22,17,23,18,10,22,24,15,15,17,16,20,23,18,but in a table data if the average expected of the class in 19-years ,so how many student are under age for the class?

How do you define "under age"… less than the mean?

Mean = sum of scores/number of scores

I'll let you do the calculations.