Kelly’s first four test grades of the period were 80 , 72 , 96 , and 88 Which inequality represents the grades she can earn on the fifth test to have a test average of no less than 80 ?

To have an average of at least 80 on five tests, the total of the five grades must be at least 5 × 80 = 400. Kelly’s first four grades total 80 + 72 + 96 + 88 = 336, so her fifth grade g must satisfy 336 + g ≥ 400. Subtracting 336 gives g ≥ 64, which is choice C, “g is greater than or equal to 64.”

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