Quantitative Aptitude and Numerical Ability
Quantitative Aptitude and Numerical Ability is arithmetic and elementary mensuration at secondary-school level, under time pressure. Expect simplification with BODMAS, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mensuration, and single-table data interpretation.
Core rules
- Percentages: memorise fraction equivalents (1/8 = 12.5%, 1/6 = 16.67%, 1/3 = 33.33%) and reduce word problems to one base quantity - take cost price as 100 or total work as the LCM.
- Profit and loss: profit per cent is always on cost price unless stated; successive discounts of a% and b% give a net a + b - ab/100.
- Interest: SI = PRT/100; for two years the gap between CI and SI is P(r/100) squared.
- Time and work: take total work as the LCM of the given days, convert each worker into units per day, then add or subtract.
- Speed: average speed over equal distances is the harmonic mean 2xy/(x+y), never the arithmetic average.
Worked example
A finishes a job in 12 days and B in 18. Working together, how long? Take total work = LCM(12, 18) = 36 units. A does 3 units a day, B does 2, together 5. Time = 36 divided by 5 = 7.2 days, that is 7 days and 4.8 hours. The trap answer 15 days comes from averaging 12 and 18.
Traps
Watch units - minutes against hours, metres against kilometres; in boats, trains and streams decide whether the stream speed or the train length is added; in mensuration check whether curved surface, total surface or volume is asked; in data interpretation read the axis scale before computing. Approximation is a tool only after the order of operations is settled.