Answer:
Step-by-step explanation:
[tex]Avg = \frac{sum}{total}[/tex]
From the problem statement, the average needs to be [tex]90[/tex], the total number of students is [tex]5[/tex], and the sum is [tex]94 + 92 + 78 + 97 + x[/tex], where [tex]x[/tex] is the grade the final student gets.
[tex]90 = \frac{94 + 92 + 78 + 97 + x}{5}[/tex]
[tex]450 = 94 + 92 + 78 + 97 + x[/tex]
[tex]450 = 361 + x[/tex]
[tex]x = 89[/tex]