Arithmetic and Quantitative Aptitude
What this domain tests
Arithmetic and Quantitative Aptitude tests numerical reasoning through percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time-work, time-speed-distance, mixtures and mensuration. The paper expects fast, accurate calculation rather than high-level mathematics.
Core rules and concepts
- Profit or loss percentage is calculated on cost price unless the question states otherwise.
- Percentage change uses the original value as the base, not the new value.
- Successive discounts are multiplied, not added: two 10% discounts give 0.9 × 0.9 = 0.81, i.e. 19% off.
- Compound interest uses A = P(1 + r/100)^n; simple interest uses SI = PRT/100.
- Time-work problems use the reciprocal of days: if A finishes in 10 days, A’s one-day work is 1/10.
- In mixtures, track the quantity that does not change, usually the solute or the milk.
Worked example
A 50 L mixture has milk and water in the ratio 4:1. Milk = 40 L and water = 10 L. If 10 L water is added, milk stays 40 L and water becomes 20 L. New ratio = 40:20 = 2:1. The trap is to add 10 L to the total ratio rather than to water alone.
Traps that cost marks
Do not add successive discounts. Do not take profit percentage on selling price unless told. Keep units consistent in speed problems. In time-work, add rates, not days.