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?
Answer & explanation
Answer: (a) 1: 3
R needs 50% copper. By alligation, P (20%) and Q (60%) must be mixed in the ratio (60 − 50) : (50 − 20) = 10 : 30 = 1 : 3.
- Equal copper and zinc means 50% copper in R.
- P : Q = (60 − 50) : (50 − 20) = 10 : 30 = 1 : 3.
- Check: 1 kg P + 3 kg Q has 0.2 + 1.8 = 2 kg copper out of 4 kg = 50%.
Remember · Alligation: ratio of cheaper to dearer = (dearer − mean) : (mean − cheaper).
Question and answer: UPSC's provisional GS Paper II (2026, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·