Quantitative Aptitude and Numerical Ability
Quantitative Aptitude and Numerical Ability tests speed and accuracy in school-level arithmetic. Recurring areas are number system, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time-work, speed-distance, mensuration and data interpretation.
Core rules
Convert every quantity to a common unit before calculating. In percentage problems, identify the base: a discount is calculated on marked price, while profit is calculated on cost price. For successive changes, multiply factors rather than adding percentages. Average speed for equal distances is the harmonic mean, not the arithmetic average. In ratio, keep the same order; in partnership, profit shares follow capital × time. For time-work, use rate = 1/time. In mensuration, write the formula before substituting.
Worked example
A shopkeeper marks an article 25% above cost and allows a 10% discount. Find profit percent. Let cost price = 100. Marked price = 125. Selling price = 125 × 0.90 = 112.5. Profit = 12.5 on cost 100, so profit = 12.5%. The single multiplier is 1.25 × 0.90 = 1.125.
Traps
Do not add 25% and subtract 10% to get 15%; do not apply discount to cost price; do not average speeds directly when times differ; and check whether interest is compounded annually or half-yearly. In data interpretation, read the units and axes before calculating.