Quantitative Aptitude and Numerical Ability
Quantitative Aptitude and Numerical Ability in AIIMS CRE tests arithmetic and data interpretation with a speed-and-accuracy bias. The syllabus is usually percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mixtures, mensuration, number system, and tabular or bar-graph DI.
Core rules
- Percentage: memorise fraction equivalents (12.5% = 1/8, 16⅔% = 1/6, 25% = 1/4). For successive changes use a + b + ab/100.
- Profit and loss: keep cost price as 100. Marked price = CP × (1 + markup). Selling price = MP × (1 − discount). Profit% is always on CP unless stated otherwise.
- Time and work: work = rate × time. For two workers, combined rate is the sum; using the LCM of days avoids fractions.
- Speed: relative speed adds for opposite directions and subtracts for same direction. Convert km/h to m/s by multiplying by 5/18.
- Interest: SI = PRT/100; CI = P(1 + r/100)^t − P.
- DI: compute only what the question asks; use approximate percentages and check the units in the legend.
Worked example
A shopkeeper marks an article 40% above cost and gives a 25% discount. What is the profit percentage? Let CP = 100. Marked price = 140. Selling price = 140 × 0.75 = 105. Profit = 105 − 100 = 5, so profit = 5%.
Traps that cost marks
Calculating discount on CP instead of MP; adding successive percentages directly; missing “per annum” or converting months to years; mixing km/h with metres; and option-trap answers that match a half-finished calculation.