A high school teacher gives three regular exams during a semester and one final exam at the end of the semester. A student’s final grade is found by taking of the student’s three regular exam scores and then adding 40% of the student’s final exam score. Sophia earned scores of 78, 92, and 80 on the three regular exams and a score of 90 on the final exam. What is Sophia’s final grade?

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.

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