GMAT Focus EditionQuantitative ReasoningEasy
A student scored 85, 92, and 78 on three exams. What score does the student need on the fourth exam to achieve an average score of 88 across all four exams?
- A92
- B97
- C95
- D88
Show answer & explanationAnswer & explanation
Correct answer: B. 97
Let the score on the fourth exam be x. The average of four exams is (Sum of scores) / 4. So, (85 + 92 + 78 + x) / 4 = 88. Summing the known scores: 85 + 92 + 78 = 255. So, (255 + x) / 4 = 88. Multiply both sides by 4: 255 + x = 352. Subtract 255 from both sides: x = 352 - 255 = 97.
Why the other options are wrong
- A. Incorrect. A score of 92 would result in an average of (255+92)/4 = 347/4 = 86.75.
- C. Incorrect. A score of 95 would result in an average of (255+95)/4 = 350/4 = 87.5.
- D. Incorrect. A score of 88 would result in an average of (255+88)/4 = 343/4 = 85.75.
Arithmetic Mean
The sum of a set of numbers divided by the count of the numbers in the set. Also known as average.
- Formula: Sum / Count = Mean.
- Used to find the central tendency of data.
- Can be used to find a missing value if the mean and other values are known.
Memory trick: Average is sum over count, a balance found.