Numerical Reasoning and Data Interpretation
This domain tests arithmetic, percentages, ratios, averages, currency and time, and your ability to interpret data presented in text, tables or charts. You must identify the question, select the right operation and work accurately under time pressure.
Core rules
- Identify the unit and the base for any percentage change.
- Distinguish percentage change from percentage points.
- Use estimation to sanity-check answers before committing.
- For successive changes, apply each percentage to the new amount, not to the original.
- Read totals, labels and footnotes; totals may not equal the sum of rounded rows.
Worked example
A division recorded 480 burglaries in Q1. Q2 was 15% lower than Q1. Q3 was 10% higher than Q2. How many burglaries were recorded in Q3? Reasoning: Q2 = 480 x 0.85 = 408. Q3 = 408 x 1.10 = 448.8. If the answer must be a whole number, 449. A common error is 480 x 0.95 = 456, which treats the two changes as a single 5% net change. That is wrong because the 10% rise applies to 408, not 480.
Traps
Adding successive percentages; applying a rise to the original base; confusing '15% lower' with '15 percentage points lower'; rounding too early; misreading which row is the total; ignoring units such as thousands or per 1,000 population.