AlgebraHardMinimum score for a target average
Algebra practice question
A student's scores on three tests are 72, 85 and 79. What is the least score the student can get on a fourth test so that the average of the four tests is at least 80?
Answer: 84
An average of at least 80 over four tests needs a total of at least 320. The three scores total 236, so the fourth must be at least 320 − 236 = 84.
Common wrong answers
- If you answered 79
- 79 is the mean of the first three tests (236/3 ≈ 78.7 rounded), not the score needed.
- If you answered 80
- 80 would give a total of 316 and an average of 79, just short.
- If you answered 324
- 324 is 80 × 4 + 4 or a similar slip; the needed total is 320, and 320 − 236 = 84.
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