16Hit1600
AlgebraMediumInequality for a minimum score

Algebra practice question

A student's marks on three tests were 72, 85, and 78. The student wants an average of at least 80 across four tests. Which inequality gives the possible marks m on the fourth test?

  1. A. (72 + 85 + 78 + m)/4 ≥ 80Correct
  2. B. (72 + 85 + 78 + m)/4 ≤ 80
  3. C. 72 + 85 + 78 + m ≥ 80
  4. D. (72 + 85 + 78)/3 + m ≥ 80

Answer: A. (72 + 85 + 78 + m)/4 ≥ 80

The average of four marks is their sum over 4, and 'at least 80' means ≥ 80. (This gives m ≥ 85.)

Why the other answers are wrong

B. (72 + 85 + 78 + m)/4 ≤ 80
'At least' means ≥, not ≤.
C. 72 + 85 + 78 + m ≥ 80
Forgets to divide by 4.
D. (72 + 85 + 78)/3 + m ≥ 80
Averages three marks and then adds the fourth, which is not the four-test average.

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