Numerical Reasoning / Data Interpretation
What this domain tests
Numerical reasoning and data interpretation test table and chart reading, percentages, ratios, averages, growth, and estimation. You must select the right operation and respect units and bases.
Core rules
- Percentage change equals (new minus old) divided by old, times 100. Always identify the base.
- Percentage points describe a difference between two percentages; percent describes relative change.
- Weighted averages require weighting by group size, not averaging the averages.
- For growth over multiple periods, multiply factors such as (1 plus r) rather than adding rates.
- Estimate before computing: round to one or two significant figures and check the answer's order of magnitude.
Worked example
A division's revenue was 4.2 million euros in 2020 and 5.04 million euros in 2021. What was the percentage growth? The change is 5.04 minus 4.2, which equals 0.84. Divide by the 2020 base: 0.84 divided by 4.2 equals 0.20, so growth is 20%. A common error is dividing by 5.04, which gives about 16.7% and uses the wrong base.
Traps
- Summing percentages across categories that overlap or have different bases.
- Reading a chart's legend or axis scale incorrectly.
- Confusing share of total with growth rate.
- Rounding too early in multi-step calculations.
- Ignoring that a table may report thousands or millions.