Water needed to reach a ratio — Aptitude Question
Water needed to reach a ratio: A 60-litre mixture contains milk and water in the ratio 7 : 3. Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
A 60-litre mixture contains milk and water in the ratio 7 : 3. How much water must be added so the ratio becomes 3 : 2?
Options
- 4 L
- 6 L
- 8 L
- 10 L
Show the answer and the worked solution
Correct answer: D. 10 L
Worked solution
- Milk = (7/10) × 60 = 42 L; water = 18 L.
- For milk : water = 3 : 2 with milk fixed at 42, water must be 42 × 2/3 = 28 L.
- Water to add = 28 − 18 = 10 L.
Answer: 10 L.
The idea
Anchor on the unchanged component, work out the new amount the other must reach, and subtract what is already present.
Shortcut. Back-check the option: 18 + 10 = 28 L of water against 42 L of milk is 3 : 2.
Common trap. 6 L — raising water from 30% to 40% of the original 60 L (24 L); adding water grows the total, so 40% of 70 L is what is needed.