Question

You are studying for a final exam of the semester. Up to this point, you received 3 exams scores of 75%,97%, and 60%. To receive a grade b in the class, you must have an average exam score between 80% and 89% for all 4 exams including the final.

Answer 1

To get an average score of 80% (out of four exams), a total of 4*80%=320% is needed, so the minimum required for the 4th test is 320-(75+97+60)=88.
To get an average score of 89% (out of four exams), a total of 4*89%=356% is needed, so the maximum required for the 4th test is 356-(75+97+60)=124, which is impossible.
So the next exam grade must range between 88 and 100 to get a grade b in the class.