Adulterated fuel — Mixtures & Alligation Aptitude Question
Adulterated fuel: A dealer mixes kerosene costing ₹40 per litre with petrol costing ₹100 per litre and sells the… Answer and worked solution on CodeKairo.
- Topic: Mixtures & Alligation
- Section: Quantitative Aptitude
- Difficulty: Hard
- Time target: 120 seconds
Question
A dealer mixes kerosene costing ₹40 per litre with petrol costing ₹100 per litre and sells the mixture at ₹100 per litre, gaining 25%. What is the ratio of kerosene to petrol?
Options
- 1 : 2
- 1 : 3
- 1 : 4
- 2 : 3
Show the answer and the worked solution
Correct answer: A. 1 : 2
Worked solution
- Required cost = 100 ÷ 1.25 = ₹80 per litre.
- Kerosene : petrol = (100 − 80) : (80 − 40) = 20 : 40 = 1 : 2.
- Checking the options against this working, the ratio is 1 : 2.
Answer: 1 : 2.
The idea
Two steps: convert the margin into a required cost, then run alligation. Skipping the first step is the usual error.
Shortcut. ₹100 at a 25% gain means a cost of ₹80; 80 is two-thirds of the way from 40 to 100, so petrol is two-thirds of the mix: 1 : 2.
Common trap. "1 : 4" — treating kerosene like free water (gain = kerosene ÷ petrol = 25%); it costs ₹40, so the mixture's cost must be found first.