UPSC CSE Prelims
Mixture & Alligation Previous Year Questions (PYQs)
Practice solved questions for Mixture & Alligation with detailed step-by-step solutions, key insights, and trend analysis for UPSC CSE PRELIMS.
Solved Previous Year Questions
Filter & practice questions topic-wise
There are two chemicals which do not react with each other. A container contains $10$ litres of the chemical $A$. One litre of this chemical is removed from it and one litre of the chemical $B$ is poured. Then one litre of the mixture is removed from the container and one litre of $B$ is poured. If this process of replacing one litre of the mixture by one litre of $B$ is performed once more, then what is the volume of $B$ that is present in the container approximately (in percentage)?
Detailed Explanation:
After each replacement of 1 litre from 10 litres, the fraction of chemical A remaining is (9/10). After 3 replacements, the amount of A left is: 10 × (9/10)³ = 10 × 729/1000 = 7.29 litres.
Since the total volume remains 10 litres, chemical B = 10 – 7.29 = 2.71 litres, which is 27.1% ≈ 27%.
Therefore, the volume of B is approximately 27%, making Option 2 the correct answer.
An alloy $P$ contains $20%$ copper and $80%$ zinc by weight. Another alloy $Q$ contains $60%$ copper and $40%$ zinc by weight. A third alloy $R$ is to be prepared from $P$ and $Q$ so that it contains equal amount of copper and zinc. In what ratio, amounts of $P$ and $Q$ be mixed in order to get $R$?
Detailed Explanation:
Use alligation method: Copper in P = 20%, in Q = 60%, desired in R = 50% (equal copper and zinc).
Ratio of P to Q = (60 - 50) : (50 - 20) = 10 : 30 = 1 : 3.
Therefore, P and Q must be mixed in the ratio 1:3, making Option 1 the correct answer.
🧐 Not Sure What to Study Next?
Get a personalised study plan based on your goals, time and revision needs.
Related Topics in CSAT (Civil Services Aptitude Test)
Frequently Asked Questions
Common questions about Mixture & Alligation in UPSC CSE PRELIMS