Question

On two tests so far this year, a student received a 78 and a 93. The student wants an average between 80 and 90 inclusive. What are all of the possible scores for the third test so that the student falls within this average?

Answer 1

240 <= 171 + x <= 270
and now subtract 171 from all and get
69 <= x <= 99
So any score from 69 to 99 will do.