Quantitative Aptitude and Numerical Ability
Quantitative Aptitude and Numerical Ability rewards clean method over long calculation: number system, HCF and LCM, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time-work and pipes, time-speed-distance, mensuration, basic algebra and data interpretation.
Shortcuts worth drilling
- Successive percentage changes combine as a + b + ab/100.
- The difference between CI and SI for two years is P(r/100) squared.
- For work problems, take the LCM of the individual times as total units, then find units per hour.
- The average of consecutive numbers equals the middle term.
- Keep units consistent - convert minutes to hours before applying a speed formula.
Worked example
One pipe fills a tank in 12 hours, another in 18 hours. How long do they take together? Reasoning: the LCM of 12 and 18 is 36, so let the tank hold 36 units. The first pipe fills 3 units per hour, the second 2 units per hour; together 5 units per hour. Time = 36 divided by 5 = 7.2 hours, which is 7 hours 12 minutes. Answer: 7 hours 12 minutes.
Traps
Quoting 7.2 hours as 7 hours 20 minutes; forgetting that an outlet or leak subtracts from filling rate; applying simple interest to a compound interest question; mixing up discount (on marked price) with profit (on cost price); ignoring a unit change in mensuration, such as centimetres against metres; rounding data-interpretation answers before reading the options.