UPSC Prelims 2026 CSAT, question 65

Topic: Arithmetic

Q65

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 $R$ ?

(a) $1:3$ Correct answer
(b) $3:1$
(c) $2:3$
(d) $3:2$

Solution.

Answer: (a) $1:3$

Alloy $P$ has $20\%$ copper, alloy $Q$ has $60\%$ copper, and the target alloy $R$ has equal amounts of copper and zinc ( $50\%$ copper).
By alligation, the required ratio of $P$ to $Q$ is $(60 - 50) : (50 - 20) = 10 : 30 = 1 : 3$ .