One number is excluded — Averages Aptitude Question
One number is excluded: The average of 5 numbers is 27. When one number is excluded the average becomes 25. Answer and worked solution on CodeKairo.
- Topic: Averages
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
The average of 5 numbers is 27. When one number is excluded the average becomes 25. What was the excluded number?
Options
- 25
- 30
- 35
- 40
Show the answer and the worked solution
Correct answer: C. 35
Worked solution
- Original total = 135; remaining total = 4 × 25 = 100.
- Excluded number = 135 − 100 = 35.
Answer: 35.
The idea
Difference of totals again. A number above the old average always pulls the average down when removed, which the answer confirms.
Shortcut. Excluded number = old average + remaining count × drop = 27 + 4 × 2 = 35.
Common trap. "30" — it looks right as 'a bit above 27', but removing 30 leaves 105 ÷ 4 = 26.25, not 25.