Step-by-step explanation:
We are told that for a large data set of a average student grades, the third quartile Q3 is found 78.5.
Since we know that third quartile represents the number such that 75% of the data is less than this number. Third quartile is the middle value between median and the highest value of a data set. Third quartile is also known as upper quartile. Third quartile splits lower 75% data from highest 25% of data.
Therefore, third quartile represents that 75% of student grades are less than 78.5 and 25% of students grades are greater than 78.5.
