Mixtures & Alligation · Question 25 · Medium
Mixtures & Alligation question 25
A 20-litre solution contains 25% acid. How many litres of it must be removed and replaced with pure acid so that the solution becomes 40% acid?
- 5 litres
- 4 litres
- 3 litres
- 6 litres
Answer and explanation
Answer: B. 4 litres
Explanation: Acid after replacing x litres = 0.25(20 − x) + x = 5 + 0.75x. Setting this equal to 40% of 20 = 8 gives 0.75x = 3, so x = 4 litres.
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