Question

Going into the final examwhich will count as two testsBrandi has test scores of 79,80, 74, 63, and 92. What score does Brandi need on the final in order to have an average score of 80?

Answer 1

86

Explanation:

You want to know the final test score Brandi needs in order to have an average of 80, given she already has scores of {79, 80, 74, 63, 92} and her final test will count as two.

Average

If her final test score is x, Brandi wants her average to be ...

(79 +80 +74 +63 +92 +2x)/7 = 80

388 +2x = 560 . . . . . . . . . multiply by 7

2x = 172 . . . . . . . . . . . . subtract 388

x = 86 . . . . . . . . . . . divide by 2

Brandi needs a score of 86 on her final to have an average of 80.

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Additional comment

Relative to her desired average, Brandi's scores are -1, 0, -6, -17, +12, for a total of -12. Since her final counts as 2 tests, she needs points on those that will bring the total to 0. -12 +2x = 0, so x=6. Her test score must be 80+6 = 86.

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