Average = (sum of the numbers)/(number of numbers)
For the juniors 80 = sum/35 so sum = 80*35 = 2800.
For the seniors 70 = sum/15 so sum = 70*15 = 1050.
The sum of the juniors scores and the seniors scores is the sum of all the scores. 2800+1050 = 3850.
Avg of all the students' scores is 3850/50 = 77
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