General Aptitude
General Aptitude in GATE NM checks verbal ability, quantitative reasoning, data interpretation, analytical deduction and spatial reasoning. The section rewards careful reading and quick, exact arithmetic; it is not a test of advanced mathematics. Most losses come from misreading the question, using the wrong base for a percentage, or averaging rates incorrectly.
Core rules
- Percentage change = (new − old)/old × 100; successive changes multiply, they do not add. A 20% rise followed by a 20% fall returns to 96% of the original.
- Ratios: convert to a common unit before comparing; for mixtures, track the actual quantity, not just the ratio.
- Average speed for equal distances is the harmonic mean, 2ab/(a + b), not (a + b)/2.
- Data interpretation: read axis labels, units and the legend; distinguish absolute values from percentages.
- Logical deduction: test each option against all statements; do not import outside assumptions.
- Verbal: watch for scope words such as all, some, only and except.
Worked example
A boat covers 36 km downstream in 3 h and the same distance upstream in 4 h. Downstream speed = 36/3 = 12 km/h; upstream speed = 36/4 = 9 km/h. Let still-water speed be b and current c. Then b + c = 12 and b − c = 9. Adding gives 2b = 21, so b = 10.5 km/h; c = 1.5 km/h. The check is that 10.5 + 1.5 = 12 and 10.5 − 1.5 = 9.
Traps
Do not average 12 and 9 to get 10.5 unless the question asks for the mean of the two speeds; here it happens to equal the boat speed because the times are symmetric in the equation, but the reasoning must come from the two equations. In percentage problems, the base changes after each step. In data interpretation, a steep-looking line may represent a small absolute change. In verbal questions, an option that is true in general but not supported by the passage is wrong.