Suppose that you are taking a course that has three exams which count for three-fifths of your grade and a final which counts for two-fifths of your grade. On your first three tests your scores on were 84, 72, and 96. To get an B in the course, you must have an average of at least 80 percent. What is the minimum score you need on the fourth test to get an B for the course?

Answer 1

(3/5)(84+72+96)/3 + (2/5)x ≥ 80
times 5
84+72+96 + 2x ≥ 400
2x ≥ 148
x ≥ 74

check:
average of first 3 tests = 84
going towards final mark = (3/5)(84) = 50.4

final mark = 74
(2/5) of that is 29.6
final mark = 50.4 + 29.6 = 80