Quantitative Aptitude
Core topics
Quantitative Aptitude here is arithmetic-dominant: number system, HCF–LCM, simplification and approximation, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, time–speed–distance, mensuration, and data interpretation from tables, bar charts and pie charts.
Fast rules to memorise
- Percentage change = (change ÷ original) × 100; the original value is always the base.
- Successive changes: net = a + b + ab/100, with discounts entered as negatives.
- Profit per cent is calculated on cost price unless the question states otherwise.
- Time and work: convert everything to one-day work; combined rate is the sum of individual rates.
- Compound interest minus simple interest for two years = P(r/100)².
- Learn squares to 30, cubes to 15, and fraction–percentage pairs (1/8 = 12.5%, 1/16 = 6.25%).
Worked example
A trader marks goods 40% above cost and allows a 25% discount. What is the profit? Let CP = 100, so MP = 140. SP = 140 × (1 − 0.25) = 140 × 0.75 = 105. Profit = 105 − 100 = 5%. Shortcut: 1.40 × 0.75 = 1.05, a 5% gain.
Traps that cost marks
- Applying the discount to cost price instead of marked price.
- Treating the second year of compound interest as simple - CI earns interest on interest.
- Unit slips in mensuration (cm versus m) and in speed (km/h to m/s: multiply by 5/18).
- Over-rounding in approximation questions until the answer no longer matches any option.
- Data interpretation: reading the wrong year or axis; compute only the value asked.
Attempt simplification and data interpretation first - they return the most marks per minute.