Mathematics / Quantitative Aptitude
Syllabus map
Number system, LCM and HCF, simplification with BODMAS, percentage, ratio and proportion, average, profit and loss, discount, simple and compound interest, time and work, pipes and cisterns, speed–distance–time, trains, boats and streams, mensuration of 2D and 3D figures, basic geometry and data interpretation.
Rules worth drilling
- Percentage change is always calculated on the original base value.
- Profit% = (SP − CP)/CP × 100; discount% is calculated on the marked price.
- Two successive discounts of a% and b% equal a + b − ab/100.
- If A finishes a job in x days and B in y days, together they take xy/(x + y) days.
- 1 km/h = 5/18 m/s.
- A train crossing a platform covers the length of the train plus the length of the platform.
Worked example
A shopkeeper marks an article 40% above cost and then allows a 25% discount. Let CP = 100, so MP = 140. Selling price = 140 × 0.75 = 105. Profit = 5 on 100, that is 5%. Note that 40% − 25% = 15% would be wrong, because the two percentages are taken on different bases (cost price versus marked price).
Traps that cost marks
- Using cost price instead of marked price when a discount is given.
- Mixing up simple and compound interest - CI is always slightly higher for the same rate and time.
- Forgetting unit conversion in time–speed questions (km/h to m/s).
- Confusing curved surface area with total surface area of a cylinder.
- Ignoring the words 'approximately' or 'nearest' when options differ only by rounding.