Business Statistics and Quantitative Aptitude
Business Statistics and Quantitative Aptitude tests numerical reasoning used in commerce: summarising data, measuring variation, and solving commercial arithmetic quickly.
Core rules
- Mean = sum of values divided by number of values. For grouped data use class midpoints. Median is the middle value after ordering; mode is the most frequent value.
- Dispersion: range, quartile deviation, mean deviation and standard deviation. Coefficient of variation = (SD / mean) × 100 and compares consistency.
- Correlation lies between -1 and +1; it measures direction and strength, not causation. Regression estimates one variable from another.
- Index numbers compare price or quantity over time. Laspeyres uses base-year quantities; Paasche uses current-year quantities.
- Commercial arithmetic: percentage change, ratio, average, simple and compound interest, profit and loss, time and work, speed and distance.
Worked example
Find compound interest on ₹10,000 at 10% per annum for two years, compounded annually. Amount = 10,000 × (1.10)^2 = 10,000 × 1.21 = ₹12,100. Compound interest = 12,100 - 10,000 = ₹2,100. Simple interest would be ₹2,000, so the extra ₹100 is interest on the first year's interest.
Traps
Use the original base when calculating percentage change, not the changed value. Average speed is total distance divided by total time, not the average of speeds. In grouped series, correct class boundaries before using median or mode formulas. Do not confuse SD with variance.