Numerical Reasoning
What this domain tests
Numerical Reasoning measures arithmetic fluency and data interpretation under time pressure: percentages, ratios, rates, averages, unit conversions and simple algebra, often set in operational contexts such as pump output, travel times, staffing or costs. A calculator may not be available, so estimation and clean unit handling matter.
Core rules
- Write the units beside every number; cancel them before calculating.
- Percentage change = change ÷ original × 100. A fall from 8 to 6 minutes is a 25% reduction, not 33%.
- Ratios scale only if every part is multiplied by the same factor.
- Rate problems: quantity = rate × time; rearrange before substituting.
- Averages: total = mean × count; weighted averages need the weights.
- Estimate first to catch order-of-magnitude errors.
Worked example
A pump delivers 1,200 L/min at full pressure. Adding a second delivery reduces the rate by 15%. How long will it take to deliver 10,200 L at the reduced rate?
Reduced rate = 1,200 × (1 − 0.15) = 1,200 × 0.85 = 1,020 L/min. Time = quantity ÷ rate = 10,200 ÷ 1,020 = 10 minutes. Check: 1,020 × 10 = 10,200. The common error is calculating 15% of the target volume or treating the 15% fall as 150 L/min.
Traps that cost marks
- Percentage increase and decrease are not symmetrical: a 20% rise needs a 16.7% fall to return to the start.
- Mixing minutes and seconds, or litres and cubic metres.
- Averaging percentages without weighting by the group sizes.
- Choosing the first answer that matches an intermediate value.