Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)

  89–100

Step-by-step explanation:

Let x represent the grade on the fifth test. The average for 5 tests wants to be between 80 and 90, so we have ...

  80 ≤ (78 +62 +91 +80 +x)/5 ≤ 90

Multiplying by 5 gives

  400 ≤ 311 +x ≤ 450

Subtracting 311 gives the range for the fifth test grade.

  89 ≤ x ≤ 139

Since the maximum available score is 100, the range on the 5th test for an overall B grade is ...

  89 ≤ x ≤ 100 . . . . where x is the grade on the 5th test

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step-by-step