General and Quantitative Aptitude
What this domain tests
General and Quantitative Aptitude covers simplification and approximation, number series, quadratic comparison, percentage, ratio, average, profit and loss, simple and compound interest, time–work and pipes, speed–distance–trains–boats, mixtures, mensuration, and - heavily weighted - data interpretation on tables, bar, line and pie charts.
Formulas that decide the paper
- CI amount A = P(1 + r/100)^n, so CI = A − P. SI = PRT/100 always uses the original principal.
- Successive discounts of a% and b% give an effective discount of a + b − ab/100, never a + b.
- If A finishes a job in x days and B in y days, together they take xy/(x + y) days.
- For equal distances travelled at x and y, average speed = 2xy/(x + y), never (x + y)/2.
- A rise and fall of the same rate r leaves a net fall of r²/100.
Worked example
₹8,000 is invested at 10% per annum compounded annually for two years. Find the compound interest. A = 8000 × (1.10)² = 8000 × 1.21 = ₹9,680. CI = 9,680 − 8,000 = ₹1,680. Shortcut for two years: CI = P[(r/100)² + 2r/100] = 8000(0.01 + 0.20) = ₹1,680, and the SI–CI gap is exactly P(r/100)² = ₹80. Checking the gap is a fast way to validate the answer.
Traps
Charging compound interest in the first year; reading 'percent more than' as 'percent of'; ignoring the units and scale of a DI chart axis; averaging two speeds arithmetically; forgetting that downstream speed is (boat + stream) and upstream is (boat − stream); and rounding early in simplification when exact cancellation was available.