Water in a mixture — Mixtures & Alligation Aptitude Question
Water in a mixture: A 50-litre mixture contains 30% water. How much milk must be added to reduce the water to 20%? Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Hard
- Time target: 90 seconds
Question
A 50-litre mixture contains 30% water. How much milk must be added to reduce the water to 20%?
Options
- 20 L
- 25 L
- 30 L
- 35 L
Show the answer and the worked solution
Correct answer: B. 25 L
Worked solution
- Water = 30% of 50 = 15 L, and it does not change.
- For water to be 20%, the total = 15 ÷ 0.20 = 75 L.
- Milk added = 75 − 50 = 25 L.
Answer: 25 L.
The idea
Anchor on the component that stays fixed — here the water — and compute the new total from it.
Shortcut. Water's share falls from 30% to 20%, so the total must grow by 30/20 = 1.5 times: 50 L → 75 L, which means adding 25 L of milk.
Common trap. "20 L" — assuming a one-third fall in the water's share needs a third more liquid (about 17 L, rounded up); the total must actually grow by half.