Quantitative Aptitude: Arithmetic Speed and Data Interpretation
Quantitative Aptitude in IDBI JAM is arithmetic-heavy. Expect simplification and approximation, number series, quadratic equations, then percentages, ratio, profit and loss, simple and compound interest, time-work, time-speed-distance, averages, mixtures and mensuration, with data interpretation (tabular, bar, pie and caselet) carrying a large block of marks.
Rules that save time
- Learn the percentage-fraction table cold: 12.5% = 1/8, 16.66% = 1/6, 6.25% = 1/16, 37.5% = 3/8. Profit, discount and DI questions usually collapse into one multiplication once converted.
- In chained ratios, equate the common term. If A:B = 2:3 and B:C = 4:5, make B = 12, giving A:B:C = 8:12:15.
- In DI, note the units and axes before computing, and approximate freely when the options are far apart.
Worked example
A trader marks goods 40% above cost and offers a 25% discount. Use successive multipliers: 1.40 × 0.75 = 1.05, so the net profit is 5% on cost. Percentages here multiply; they never simply add or subtract.
Traps
- Applying the discount to the selling price instead of the marked price.
- Mixing simple and compound interest formulas, or compounding for the wrong number of periods.
- In time and work, adding day-counts instead of rates; convert "A finishes in 12 days" to 1/12 per day first.
- Ignoring the "approximately" instruction and doing exact long division in simplification sets.