General Aptitude: Numerical Reasoning for Operational Problems
The General Aptitude section tests numerical reasoning under time pressure: percentages, ratio and proportion, averages, time-speed-distance, profit and loss, interest, number series and data interpretation from tables and charts.
Core rules
- Percentage change equals (new minus old) divided by old, multiplied by 100. Successive changes multiply rather than add.
- Work and time: combined rate is the sum of the individual rates.
- Average speed is total distance divided by total time; it equals the arithmetic mean of two speeds only when the two times are equal.
- Compound interest is P(1 + r/n) raised to nt, minus P.
- Ratio split: multiply the total by each part and divide by the sum of the parts.
- Series patterns: first differences, then ratios, then squares, cubes or alternating rules.
Worked example
An aircraft flies 1,200 NM outbound at 400 kt true airspeed into a 50 kt headwind, then returns with a 50 kt tailwind. Outbound ground speed is 350 kt and the time is 1,200 divided by 350, about 3.43 h. Return ground speed is 450 kt and the time is 1,200 divided by 450, about 2.67 h. Total time is 6.10 h for 2,400 NM, so average ground speed is 2,400 divided by 6.10, about 393.6 kt. The arithmetic mean of 400 kt is wrong because more time is flown at the slower speed.
Traps
Averaging speeds arithmetically; mixing units (1 m/s is 3.6 km/h; 1 NM is 1.852 km); reading percentage points as per cent; treating successive discounts of 20 per cent and 10 per cent as 30 per cent instead of 28 per cent; rounding too early in a multi-step answer.