Combining two groups — Averages Aptitude Question
Combining two groups: The average of 30 results is 20 and the average of 20 other results is 30. Answer and worked solution on CodeKairo.
- Topic: Averages
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 50 seconds
Question
The average of 30 results is 20 and the average of 20 other results is 30. What is the average of all 50?
Options
- 23
- 24
- 25
- 26
Show the answer and the worked solution
Correct answer: B. 24
Worked solution
- Totals: 30 × 20 = 600 and 20 × 30 = 600.
- Combined = 1,200 over 50 results.
- Average = 24.
Answer: 24.
The idea
A combined average is total ÷ total count, never the mean of the two averages. Here the plain mean would give 25, which is offered.
Shortcut. Start at 20 and move towards 30 in proportion to the second group's share: 20 + 10 × 20/50 = 24.
Common trap. "25" — averaging 20 and 30 as if the groups were the same size; the 30 results at 20 outweigh the 20 at 30.