Numerical Reasoning and Quantitative Problem Solving
What is actually tested
Numerical reasoning items ask you to pull quantities out of short passages or tables and act on them correctly under time pressure. The toolkit is small: percentages and percentage change, ratios and proportions, rates (per hour, per unit, per head), averages including weighted averages, and simple unit or currency conversion. Success comes from recognising which operation a wording cue demands, not from advanced mathematics.
The recurring traps
The commonest is percent versus percentage points. A rate rising from 8% to 10% has risen 2 percentage points but 25%. The second is direction and chaining: a price that falls 30% then rises 30% does not return to its start - multiply the multipliers, 0.70 x 1.30 = 0.91, a net 9% loss. The third is averages of averages: combining two groups requires weighting by group size, or your answer is wrong but plausible. The fourth is unit mismatch - minutes against hours, pence against pounds, thousands against millions. The fifth is the distractor built from the wrong operation: the sum when the question asked for a difference.
Worked example
Six people process 240 cases in 4 days. How long will nine people take to process 540 cases at the same rate? Rate per person-day = 240 / (6 x 4) = 10 cases. Person-days needed = 540 / 10 = 54. Days = 54 / 9 = 6.
Rule of thumb
Write the units before the arithmetic - "cases per person per day" - and cancel them as you go. If the units of your answer are not the units requested, stop: you have made the classic error. Estimate first, then calculate, then sanity-check the magnitude against your estimate.