Quantitative Aptitude and Reasoning
This domain tests numerical ability and logical reasoning at a practical level: arithmetic, mensuration, data interpretation, series, coding, relations, directions and syllogisms. Speed comes from recognising standard patterns, not from long calculation.
Core rules
- Percentage change: use the original quantity as the base; successive changes are not additive.
- Profit and loss: keep cost price as 100 when a discount is given on marked price.
- Simple and compound interest: SI = PRT/100; CI compounds each period.
- Time and work: convert days to work per day; combine rates by addition.
- Speed: average speed for equal distances is the harmonic mean, not the arithmetic mean.
- Reasoning: draw family trees, direction diagrams and Venn diagrams; for syllogisms, test the conclusion against all possible diagrams.
Worked example
A shopkeeper marks an article 25% above cost and gives a 10% discount. Find profit percent. Let CP = 100. MP = 125. SP = 125 × 0.90 = 112.5. Profit = 12.5 on 100, so 12.5%. The discount is on MP, not CP; applying 10% to CP would give the wrong answer.
Traps
- Adding successive percentage changes: 25% up then 20% down is not 5% net.
- Using SP instead of CP as the profit base.
- Averaging speeds arithmetically over equal distances.
- Reversing “some” and “all” in syllogisms.
- Ignoring units in mensuration and data interpretation.