General Mathematics and Mental Ability
Core concepts
This section rewards speed with accuracy: arithmetic (percentage, profit-loss, ratio, average, simple and compound interest, time-work, speed-distance), elementary algebra, basic geometry and mensuration, and mental ability (number series, analogy, coding-decoding, direction sense, blood relations, odd-one-out, clock and calendar).
Traps
Percentage questions hide the base: a 20% rise followed by a 20% fall does not return to the original value (net 4% fall). Profit-loss problems confuse cost price with selling price when a discount is given. Time-work questions fail if rates are added instead of reciprocals. In series questions, two interleaved patterns often run at once. In direction sense, candidates forget that turning left after facing south changes the axis. Calendar problems require knowing the odd-day count of a century.
Rule of thumb and worked example
For successive percentage change, use net = a + b + ab/100. Example: +20% then -20% gives 20 - 20 + (20 × -20)/100 = -4%, i.e. a 4% decrease. For work, if A finishes in 12 days and B in 6, together they do 1/12 + 1/6 = 1/4 per day, so 4 days. For average, remember total = average × count; adding a value changes the total, not just the average.
Speed strategy
Estimate before computing, eliminate options by unit or magnitude, and keep a rough answer ready so a small arithmetic slip does not cost the question.