Numerical Reasoning: Speed, Estimation and Ratio Sense
Numerical items under time pressure reward structure over arithmetic. The concepts you need are: ratios and proportion, percentages and percentage change, rates (speed, work, flow), averages and weighted averages, unit conversion, and reading tables and graphs accurately. Most questions can be solved by setting up a relationship and cancelling, not by long division.
The traps are predictable. Percentage points versus percent (a rise from 20% to 25% is 5 points but a 25% increase). Averaging averages without weighting for group size. Reversing a percentage change (a 20% rise is undone by a 16.7% fall, not a 20% fall). Unit mismatch - minutes against hours, metres against kilometres. Distractor answers built from the wrong operation, so a plausible number appearing mid-calculation is a warning, not a comfort. Finally, check whether a question asks for a total, a difference, or a rate.
Rule of thumb: estimate first to one significant figure, eliminate, then compute exactly only if two options survive. Sanity-check magnitude: if a train's average speed comes out at 400 km/h, re-read the units.
Worked example: A team of 6 completes a task in 10 days. After 4 days, 2 leave. Remaining work = 6 × 6 = 36 person-days; now 4 people, so 36 ÷ 4 = 9 further days; total 13 days.