Quantitative Aptitude and Numerical Ability
Syllabus weight
Quantitative Aptitude covers the number system, HCF–LCM, percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time–work and pipes, speed–time–distance, mixtures and alligation, mensuration, basic algebra, geometry, trigonometry and data interpretation through tables, bar and pie charts.
Rules worth memorising
- Percentage change = (change/original) × 100; successive changes multiply: a% then b% gives a + b + ab/100.
- Profit% is on cost price unless stated otherwise; discount is always on marked price.
- CI = P[(1 + r/100)^n − 1]; for half-yearly compounding, halve r and double n.
- Work: if A finishes in x days, one day's work is 1/x; combined rates add.
- Speed conversion: 1 km/h = 5/18 m/s.
Worked example
A trader marks an article 40% above cost and allows a 25% discount. Find the profit percentage. Let CP = 100. MP = 140. SP = 140 × 0.75 = 105. Profit = 5 on CP 100, so profit% = 5%. The discount applies to MP, not CP; applying 25% to CP would wrongly give 15% profit.
Traps
- Adding successive percentages (40 − 25 = 15) instead of multiplying.
- Mixing SI and CI for periods longer than one year.
- Unit mismatch in speed–distance questions, such as minutes versus hours.
- In data interpretation, misreading the axis scale or a total row.