Blending a 60% and a 20% copper alloy — Aptitude Question
Blending a 60% and a 20% copper alloy: Alloy A contains 60% copper and alloy B contains 20% copper. Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
Alloy A contains 60% copper and alloy B contains 20% copper. In what ratio must they be mixed to obtain an alloy with 45% copper?
Options
- 3 : 5
- 5 : 3
- 4 : 3
- 3 : 4
Show the answer and the worked solution
Correct answer: B. 5 : 3
Worked solution
- A : B = (45 − 20) : (60 − 45) = 25 : 15 = 5 : 3.
- Check: (5 × 60 + 3 × 20)/8 = 360/8 = 45. ✓
Answer: 5 : 3.
The idea
Take care with the direction: the quantity of the richer alloy is proportional to (mean − poorer). The mean at 45 is nearer 60, so more of A is needed.
Shortcut. 45% is nearer 60%, so A must be the larger share — only 5 : 3 and 4 : 3 qualify, and 4 : 3 gives (240 + 60) ÷ 7 ≈ 42.9%, so 5 : 3.
Common trap. 3 : 5 — pairing each alloy with its own distance from 45 (15 for A, 25 for B) instead of crossing them; that mix is only 35% copper.