Blending two alloys — Aptitude Question
Blending two alloys: Alloy A is 40% copper and alloy B is 70% copper. In what ratio should they be melted together… Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
Alloy A is 40% copper and alloy B is 70% copper. In what ratio should they be melted together to give an alloy that is 50% copper?
Options
- 3 : 2
- 1 : 1
- 2 : 1
- 1 : 2
Show the answer and the worked solution
Correct answer: C. 2 : 1
Worked solution
- A : B = (70 − 50) : (50 − 40) = 20 : 10 = 2 : 1.
- Check: (2 × 40 + 1 × 70)/3 = 150/3 = 50. ✓
Answer: 2 : 1.
The idea
Percent concentrations obey the same alligation cross as prices. The target closer to A means more of A.
Shortcut. 50 lies a third of the way from 40 to 70, so alloy B is a third of the blend: A : B = 2 : 1.
Common trap. 1 : 2 — putting the gaps the wrong way round (10 : 20); the target 50 is nearer A's 40, so there must be more of A.