Quantitative Aptitude: Speed Arithmetic and the Base-Value Discipline
Core toolkit
Quantitative Aptitude in a BBA entrance test is speed arithmetic, not higher mathematics. Master: percentages and their fraction equivalents (12.5% = 1/8, 16.66% = 1/6, 20% = 1/5), ratio and proportion, averages and weighted averages, profit–loss and discount, simple and compound interest, time–speed–distance, time and work, basic permutations and probability, mensuration, and data interpretation (tables, bar, pie and line charts).
Recurring traps
- Percentage change is always calculated on the base: a 20% rise followed by a 20% fall is a net 4% fall, not zero.
- Successive discounts of a% and b% give a + b − (ab/100), never a + b.
- "Increased by 25%" versus "increased to 125%" are different statements read identically by careless candidates.
- Unit mismatch - minutes versus hours, metres versus kilometres - is the most common silent error.
- In time and work, add rates (1/x + 1/y), never times.
- Data interpretation often needs one ratio, not the full computation; approximate and compare with the options.
Worked example
A shop offers 20% and then 10% off. Net discount = 20 + 10 − (20 × 10)/100 = 28%. A ₹1,500 item therefore sells for ₹1,080, not ₹1,050.
Rule of thumb
Convert percentages to fractions before calculating, and estimate the rough size of the answer first. If your result misses by a factor of 10 or 60, you have almost certainly hit a unit trap rather than a calculation error.