Numerical and Data Interpretation
These items test reading numbers accurately and reasoning about them, not advanced mathematics. Know: percentages versus percentage points, percentage change and the effect of the base value, ratios and proportions, rates (per hour, per 1,000 travellers), averages - mean, median, and when an outlier distorts the mean - unit conversion, weighted averages, and reading tables and graphs correctly, including axis scales, legends, units, and whether a trend can legitimately be extrapolated beyond the data shown.
Traps are everywhere. Confusing a rise from 20% to 25% with "a 5% increase" (it is 5 percentage points, or a 25% relative increase). Assuming a 20% increase followed by a 20% decrease returns to the starting value (it does not). Using the wrong denominator - comparing a share of all travellers with a share of referred travellers. Reading a truncated or mislabelled axis as if it started at zero. Averaging two averages without weighting them by their group sizes. And answering a question that was not asked because a nearby number looked familiar.
Rule of thumb: write the units beside every number and estimate the answer before computing; if your exact result is far from your estimate, you have probably misread a scale or a denominator.
Worked example: 240 travellers arrive; 15% are referred for secondary examination, and one quarter of those are found inadmissible. Referred: 240 × 0.15 = 36. Inadmissible: 36 ÷ 4 = 9. As a share of all travellers, that is 9 ÷ 240 = 3.75%. Note how the question's wording decides which denominator you use.