Quantitative Aptitude / Elementary Mathematics
Quantitative Aptitude / Elementary Mathematics
This domain checks speed and accuracy on school-level arithmetic: number system, percentage, ratio, average, profit and loss, simple and compound interest, time-work, speed-distance, mensuration, simplification, and data interpretation.
Core rules
- Percentage: change % = (change / original) x 100. For successive changes use multipliers, e.g. +20% then -10% = 1.20 x 0.90 = 1.08, a net +8%.
- Ratio: convert to parts; if A:B = 3:5 and total is 64, one part = 8, so A = 24 and B = 40.
- Average: sum = average x number of items. When a new item is added, compare the new total with the old total.
- Work: if A finishes in a days and B in b days, together they take ab/(a+b) days. Use rates, not times, when adding workers.
- Speed: distance = speed x time; for a train crossing a platform, total distance = train length + platform length.
- Mensuration: keep units consistent; convert cm to m before area/volume.
Worked example
A sum doubles in 8 years at simple interest. In how many years will it become four times? Doubling means interest = P in 8 years, so the annual SI rate is 100%/8 = 12.5%. To become four times, interest must be 3P. At 12.5% per year, 3P requires 3 x 8 = 24 years. The trap is applying compound interest; the question says simple interest.
Traps
Calculating percentage on the new value instead of the original; mixing SI and CI; forgetting that '4 times' means 3P interest, not 4P; and ignoring unit changes in mensuration.