Answer:
89
Step-by-step explanation:
Given that the class has 28 students has 7 juniors and 21 seniors
mean score of the juniors = 73
Therefore, total score of junior = 73 × 7
= 511
mean score of seniors = y
Total score of seniors = 21y
Total score of the class = 511 + 21y
Mean score of the class = 85
Total score of the class = 85 × 28
= 2380
therefore,
511 + 21y = 2380
21y = 2380 -511
21y = 1869
y = 1869/21
y = 89
