Two classes together — Averages Aptitude Question
Two classes together: A class of 30 students averages 40 marks and another of 50 students averages 60 marks. Answer and worked solution on CodeKairo.
- Topic: Averages
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
A class of 30 students averages 40 marks and another of 50 students averages 60 marks. What is the combined average?
Options
- 50
- 52.5
- 54
- 55
Show the answer and the worked solution
Correct answer: B. 52.5
Worked solution
- Totals: 30 × 40 = 1,200 and 50 × 60 = 3,000.
- Combined total = 4,200 over 80 students.
- Average = 4,200 ÷ 80 = 52.5.
Answer: 52.5.
The idea
The combined average leans towards the larger group — here towards 60, so above the midpoint of 50. That is a useful check on the answer.
Shortcut. Start at 40 and move towards 60 by the larger class's share: 40 + 20 × 50/80 = 52.5.
Common trap. "50" — the plain mean of 40 and 60, which ignores that the 50-student class pulls the result towards 60.