Copper in two alloys — Aptitude Question
Copper in two alloys: Alloy P is 30% copper and alloy Q is 60% copper. In what ratio must they be mixed to obtain… Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
Alloy P is 30% copper and alloy Q is 60% copper. In what ratio must they be mixed to obtain 40% copper?
Options
- 1 : 2
- 2 : 1
- 2 : 3
- 3 : 2
Show the answer and the worked solution
Correct answer: B. 2 : 1
Worked solution
- P : Q = (60 − 40) : (40 − 30) = 20 : 10 = 2 : 1.
- Check: (2 × 30 + 1 × 60)/3 = 120/3 = 40. ✓
Answer: 2 : 1.
The idea
The mean at 40 is nearer 30, so more of the poorer alloy is needed. Checking the direction before computing avoids inverting the ratio.
Shortcut. 40 is a third of the way from 30 to 60, so the mixture is two-thirds alloy P: 2 : 1.
Common trap. "1 : 2" — pairing each alloy with its own distance from 40 (10 : 20); each share goes with the other alloy's distance.