Blending two acid solutions — Aptitude Question
Blending two acid solutions: A 20% acid solution is mixed with a 50% acid solution to give 30% acid. Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
A 20% acid solution is mixed with a 50% acid solution to give 30% acid. In what ratio are they mixed?
Options
- 1 : 2
- 2 : 1
- 3 : 2
- 2 : 3
Show the answer and the worked solution
Correct answer: B. 2 : 1
Worked solution
- Weaker : stronger = (50 − 30) : (30 − 20) = 20 : 10 = 2 : 1.
- Check: (2 × 20 + 1 × 50)/3 = 90/3 = 30. ✓
Answer: 2 : 1.
The idea
Alligation works identically for prices, percentages and rates. Always verify by taking the weighted average of your answer.
Shortcut. 30% is a third of the way from 20% to 50%, so the strong solution is a third of the mix: 2 : 1.
Common trap. "1 : 2" — setting each solution against its own distance from 30% (10 : 20), which inverts the ratio.