Quantitative Aptitude and Numerical Ability
Syllabus map
Quantitative Aptitude rewards a fixed set of standard tools: simplification and approximation; number system (HCF, LCM, divisibility, remainders); percentage; ratio and proportion; averages; profit, loss and discount; simple and compound interest; time and work, pipes and cisterns; speed, distance, trains and boats; mixtures and alligation; mensuration (2D and 3D); basic geometry and trigonometry; permutation, combination and probability; and data interpretation on tables, bar, line and pie charts.
Traps
Most errors come from using the wrong base. A 20% increase followed by a 20% decrease is not zero but a 4% net decrease. Successive discounts of 20% and 10% are not 30%. In time and work, adding a worker changes the rate, not the time, so convert everything to work-per-day. For compound interest, the rate applies to the accumulated amount, so CI exceeds SI by the interest-on-interest component. Convert km/h to m/s by multiplying by 5/18, and check units before marking.
Worked example
A shirt marked at ₹1,000 gets successive discounts of 20% and 10%. Do not add: 1,000 × 0.80 = 800, then 800 × 0.90 = 720. Total discount is ₹280, i.e. 28%. The single equivalent discount for a% and b% is a + b − ab/100.
Rule of thumb: in data interpretation, read the axes and units first and use approximation - the options are usually spaced far apart.