Quantitative Aptitude and Reasoning
Quantitative Aptitude and Reasoning tests numerical accuracy and logical structure under time pressure. Numerical topics include percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time–work, speed–distance, and data interpretation. Reasoning topics include series, coding–decoding, blood relations, directions, syllogism, seating arrangement, and analogies.
Core rules
- Percentage change: a rise of r% followed by a fall of r% gives a net change of −r²/100%, not zero.
- Ratio: convert to a common unit before comparing; keep the same base for every term.
- Average: total = average × number of items; adding a value shifts the average by the value’s deviation divided by the new count.
- Syllogism: draw only conclusions that must follow from the premises; “some” does not imply “all”.
- Direction sense: fix one reference direction and track left/right turns sequentially.
Worked example
A clerk’s salary is increased by 20% and then reduced by 20%. What is the net change? Take the original salary as 100. After a 20% rise: 100 × 1.20 = 120. After a 20% fall on 120: 120 × 0.80 = 96. Net change = 96 − 100 = −4, so a 4% decrease. The second percentage applies to the new amount, not the original; that is why the answer is not zero.
Traps that cost marks
Using the old base after an increase; ignoring units in speed–distance; treating “either–or” as “both”; and assuming a diagram in seating arrangement before fixing all constraints.