Quantitative Aptitude
Quantitative Aptitude in OICL AO tests arithmetic and data interpretation under time pressure: percentage, ratio, average, profit and loss, simple and compound interest, time-speed-distance, mixtures, probability, number series, simplification and DI (table, bar, pie and caselet).
Core rules
- Percentage changes multiply: a 20% rise then 10% fall is 1.20 x 0.90 = 1.08, an 8% net rise, not 10%.
- In SI, interest is on principal only; in CI, use (1 + r/100)^n.
- In DI, read the unit and base before calculating; percentage-point change differs from percentage change.
- Approximation is safe only after checking that options are far apart.
Worked example
A sum doubles in 8 years at simple interest. Find the annual rate. Reasoning: Let principal be P. Amount = 2P, so SI = P. SI = P x r x 8 / 100. Thus P = 8Pr/100, giving r = 100/8 = 12.5% per annum. Check: 12.5% of P for 8 years = P, so amount = 2P.
Traps
Using the CI formula for SI; taking doubles as 100% interest over 8 years but then dividing by 8 incorrectly; in DI, adding percentages from different bases; in series, forcing one pattern when two operations alternate.