Numerical Aptitude and Elementary Mathematics
Numerical Aptitude and Elementary Mathematics tests speed and accuracy on school-level arithmetic; the difficulty is time, not concept depth.
Syllabus core
- Percentage and its applications, including successive change.
- Ratio, proportion and partnership.
- Average, mixture and alligation.
- Profit, loss and discount; simple and compound interest.
- Time–speed–distance, trains and boats.
- Time and work, pipes and cisterns.
Formulas worth memorising
- Successive change: net % = a + b + (ab ÷ 100).
- Compound interest minus simple interest for two years = P(r/100)².
- Two workers together: 1/T = 1/A + 1/B.
- km/h to m/s: multiply by 5/18.
- Average speed for equal distances = 2xy ÷ (x + y).
Worked example
A finishes a job in 12 days and B in 18 days. How long together? Reasoning: take total work as LCM(12, 18) = 36 units. A does 3 units a day and B does 2, so together 5 units a day. Time = 36 ÷ 5 = 7.2 days, that is 7 days and 4 hours 48 minutes. The fraction method agrees: 1/12 + 1/18 = 5/36, so T = 36/5.
Traps
- Treating a 20% rise followed by a 20% fall as no change; the net is a 4% fall.
- Applying the simple interest formula to a compound interest question.
- Averaging two speeds directly instead of using total distance divided by total time.
- Forgetting to convert minutes to hours in time–speed questions.