Numerical Reasoning and Data Interpretation
Numerical reasoning tests your ability to pull the right number from tables, rosters, and reports and apply it correctly under time pressure. The concepts you must control are percentages and percentage change, ratios and rates, averages (mean) versus totals, unit conversion (hours to shifts, days to weeks), and reading row/column headers carefully.
Common traps: confusing percentage points with percent (a rate rising from 20% to 25% is a 5 percentage-point rise but a 25% relative increase); using the wrong denominator (per officer versus per shift); averaging averages instead of weighting by group size; and ignoring a 'total' row that already contains the figures you are adding. Also watch for questions asking for a value before a change - you must reverse the calculation.
Rule of thumb: write down the units before you calculate, and sanity-check that your answer is plausible (a percentage of a population cannot exceed 100%; a rate cannot be negative).
Worked example: A unit has 40 officers across 5 shifts; 25% are on night shift. How many officers is that? 25% of 40 = 10 officers. If 2 of those are reassigned, the night shift falls to 8, which is 20% of 40 - a 5 percentage-point drop but a 20% relative reduction. State which one the question wants.