Quantitative Aptitude
Quantitative aptitude tests arithmetic and numerical reasoning: percentages, ratio and proportion, averages, time–work, profit–loss, simple interest and data interpretation. Accuracy under timed conditions depends on choosing a short method.
Core rules
- Percentage change = (new − old) ÷ old × 100. A 20% increase followed by a 20% decrease leaves 96% of the original, not 100%.
- Ratio: express quantities in the same unit before simplifying. For a:b = 2:3, parts are 2x and 3x.
- Time and work: if A finishes in a days and B in b days, together they take ab/(a+b) days. Work rate = 1/time.
- Average = sum ÷ number; if every item increases by k, the average increases by k. Profit% is calculated on cost price unless stated otherwise.
Worked example
A finishes a task in 10 days and B in 15 days. LCM of 10 and 15 is 30 units. A does 3 units/day, B does 2 units/day; together 5 units/day. Time = 30 ÷ 5 = 6 days. Reasoning: converting to units avoids fractions and makes combined rates additive.
Traps
Using the wrong base in percentage change; adding times instead of rates; forgetting unit conversion in ratio questions; calculating profit on selling price when the question says cost price.