Numerical Reasoning and Data Interpretation
What this domain tests
Numerical reasoning and data interpretation test your ability to work with percentages, ratios, rates, averages and tables. Questions are usually set in an operational context: application volumes, refusal rates, backlog, processing times, staffing and costs. You are tested on the calculation and on choosing the right base.
Core rules
- Identify the base before calculating a percentage. A 20% rise followed by a 20% fall does not return to the original value.
- Distinguish percentage change from percentage points. A refusal rate moving from 12% to 15% is a 3 percentage-point rise, not a 3% rise.
- For weighted averages, weight by the relevant population. Do not average two group averages unless the groups are the same size.
- Read axes, units and footnotes. Convert days to weeks or currency before combining.
- Round only at the end. Early rounding can change the answer option.
- Check whether a figure is cumulative (year to date) or for a single period.
Worked example
A centre receives 1,200 applications in a month. Of these, 15% are refused. Of the refused applications, 60% request a review, and 25% of those reviews are upheld. How many refusals are overturned? Refused: 1,200 x 0.15 = 180. Reviews requested: 180 x 0.60 = 108. Upheld: 108 x 0.25 = 27. Answer: 27. The common error is calculating 25% of 180 (45), which ignores that only 60% requested review.
Traps
- Taking a percentage of the wrong total, especially after a subgroup is introduced.
- Adding percentages that apply to different bases.
- Treating 'percentage points' and 'percent' as interchangeable.
- Using the average of two averages without checking group sizes.
- Forgetting unit conversions, such as working days versus calendar days.
- Selecting an answer that matches an intermediate step rather than the final question.