Numerical Aptitude and Reasoning
The tested areas
Arithmetic: percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, ages, partnership, basic mensuration. Reasoning: number and letter series, coding-decoding, blood relations, direction sense, syllogism, seating arrangement, analogy, classification, and calendar/clock basics.
Core rules to apply
- Percentage change: successive changes multiply, they do not add. A rise of a% then a fall of b% gives a net change of a − b − ab/100.
- Average: total ÷ count. If every item is increased by k, the average rises by k.
- Time and work: convert days to units of work per day (LCM method) to avoid fractions.
- Blood relations: draw a small family tree and mark gender with symbols before answering.
- Syllogism: a conclusion is valid only if it holds in every possible diagram of the premises.
Worked example. A beneficiary count is increased by 20% and then reduced by 20%. What is the net change? Reasoning: start with 100. A 20% rise gives 120. A 20% fall is calculated on 120, i.e. 24, giving 96. Net change = 100 → 96 = 4% decrease, matching the formula 20 − 20 − (20×20)/100 = −4.
Traps that cost marks
- Adding successive percentages instead of multiplying them.
- Averaging averages without weighting by group size.
- Assuming a syllogistic conclusion is true because it looks plausible rather than because it follows necessarily.
- Forgetting that in direction questions a left or right turn depends on the facing direction.