Numerical Ability and Quantitative Aptitude
What the section tests
Numerical Ability checks speed and accuracy with school-level arithmetic: simplification, HCF/LCM, percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time-work, time-speed-distance, mensuration and basic data interpretation. Questions are usually short; the difficulty lies in choosing the fastest method.
Rules that save time
- Convert fractions to percentages: 1/8 = 12.5%, 1/6 = 16.67%, 1/12 = 8.33%.
- Profit% and loss% are always calculated on cost price unless stated otherwise.
- Discount is always on marked price.
- For successive changes use a + b + ab/100; a 20% rise then 10% fall gives 20 − 10 − 200/100 = 8% net rise.
- In time-work, take total work as the LCM of the days given.
Worked example
A shopkeeper marks an article 40% above cost and allows a 25% discount. Find the profit%. Let CP = 100. Marked price = 140. Selling price = 140 × (75/100) = 105. Profit = 105 − 100 = 5, so profit% = 5/100 × 100 = 5%. Common wrong method: 40 − 25 = 15% profit, which ignores that the discount applies to the marked price, not the cost price.
Traps
- Applying discount to CP instead of MP.
- Adding successive percentages directly.
- Mixing units (km/h with metres, minutes with hours).
- Averaging two averages without weighting by group size.