Astudent has scores of 72%, and 78% on three mathematics examinations. what interval of scores does his last score need to fall in to earn a grade of b (80% or better)?

The student wants a grade of x on his 3rd exam, so that the average of the 3 exam grades is 80:

72 + 78 + x

= 80

3

Solving for x: 72 + 78 + x = 240, or x = 90

If the student earns a grade of 90 or better on the 3rd exam, he will earn a course grade of 80 or better.

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