Numerical Ability: Set Up the Base Before Calculating
Numerical Ability / Quantitative Aptitude checks percentage, ratio, average, profit and loss, simple and compound interest, time-work, speed-distance, mensuration, number system, simplification, and data interpretation. Most questions reward a clean setup more than long calculation.
Core rules
- Percentage change = (change ÷ original) × 100; the base must be the original value.
- Successive discounts are multiplied, not added.
- Profit% and loss% are calculated on cost price unless stated otherwise.
- Work: combined one-day work = sum of individual one-day work.
- Speed: convert km/h to m/s by multiplying by 5/18.
Worked example
A shopkeeper marks an article 40% above cost and gives successive discounts of 10% and 5%. Find the profit percent. Reasoning: Let CP = 100. Marked price = 140. After 10% discount: 140 × 0.90 = 126. After 5% discount: 126 × 0.95 = 119.70. Profit = 119.70 − 100 = 19.70. Profit% = 19.7%.
Traps that cost marks
- Adding 10% and 5% to get 15%; successive discounts compound.
- Taking the marked price as the base for profit%.
- Mixing minutes and hours in time-work or speed questions.
- Rounding too early in data interpretation.
- Ignoring units in mensuration (cm vs m).