Diluting an acid solution — Aptitude Question
Diluting an acid solution: How much water must be added to 40 L of a 30% acid solution to make it a 20% solution? Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
How much water must be added to 40 L of a 30% acid solution to make it a 20% solution?
Options
- 10 L
- 15 L
- 20 L
- 25 L
Show the answer and the worked solution
Correct answer: C. 20 L
Worked solution
- Acid = 30% of 40 = 12 L, and it stays 12 L.
- New total = 12/0.2 = 60 L.
- Water added = 60 − 40 = 20 L.
Answer: 20 L.
The idea
Dilution keeps the solute fixed. Solute ÷ new concentration = new total volume; subtract the old volume.
Shortcut. Strength falls from 30% to 20%, a factor of 2/3, so the volume must grow by 3/2: 40 L → 60 L, add 20 L.
Common trap. 10 L — matching the 10-point drop in strength; 12 L of acid in 50 L is still 24%, so 20 L are needed.