Civil Service Numerical Test common mistakes
Civil Service Numerical Test · Understand the traps and how to avoid them.
Works through a multi-step calculation, reaches a meaningful intermediate figure (such as the pre-tax subtotal or the monthly rather than annual amount), and writes that down as the final answer without finishing the last operation.
Under time pressure the brain treats 'I have produced a number' as task completion, and the final transformation feels like a formality rather than a step that can be got wrong.
What to do instead
Before starting, underline the exact quantity requested in the stem and write it as a target at the top of the working space. After computing, physically re-read the stem and label the last line of working with both a unit and the words 'this is the answer', then check that label against the underlined target.
Adds successive percentage changes instead of compounding them, so a 20% increase followed by a 10% decrease is reported as a net 10% increase.
Single-change percentage work is drilled until it becomes automatic, and the additive shortcut generalises silently because the two changes look like separate, stackable amounts.
What to do instead
Convert every change into a multiplier before touching the figures (1.20 and 0.90), multiply the multipliers together, and only then convert back to a percentage. Add a direction check: ask whether the final value should sit above or below the starting value, and reject any answer that contradicts it.
Tracks along a row of a dense table with the eyes while the reference point drifts, pairing a figure with the wrong column or with the header one line above or below the intended one.
Tables with similar repeated headers, merged cells and blanks give the eye weak visual anchors, and the reading hand usually stops moving before the eye does.
What to do instead
Use a pen or a folded edge of paper as a straight edge under the relevant row, and before using any cell, restate it aloud or in writing as a full sentence such as 'Region B, 2019, thousands of units'. If the restatement is awkward, the cell has been misread.
Performs arithmetic with mixed units inside a single calculation, for example dividing a distance given in metres by a time given in minutes and then reporting the result as kilometres per hour.
The question supplies data in whatever units suit the scenario, and the numbers themselves divide cleanly, so nothing in the arithmetic signals that the units are incompatible.
What to do instead
At the start of the question, write the conversion factor next to each figure and restate every value in one chosen base unit before calculating. At the end, convert the result back into the unit the question actually asks for and check that the size of the answer is plausible for that unit.
Averages a set of rates by adding the individual rates and dividing by how many there are, giving equal weight to a two-hour journey and a twenty-minute one.
The word 'average' triggers the familiar arithmetic-mean routine, and the weighting issue is invisible unless the times or distances involved are explicitly compared.
What to do instead
Before averaging any rate, identify what the weights are (time for speed, distance for fuel consumption, quantity for price per unit). Use total amount divided by total weight, and sanity-check that the result lies between the smallest and largest individual rate, pulled towards the one covering the greater share.
Estimates an answer by rounding every number in the same direction, so that four figures each rounded up push the estimate well past the true value and none of the offered options matches it closely.
Rounding up feels like the cautious, default habit, and the cumulative drift is not obvious when each individual rounding step looks trivial.
What to do instead
Round to one significant figure but deliberately push some values up and others down to offset the drift, or move to two significant figures when the answer options are tightly spaced. Finish by computing a rough exact value so the estimate can be checked against a known ballpark rather than accepted on trust.
Loses a decimal place or a trailing zero when multiplying or dividing by 10, 100 or 1000, or when working with money expressed in pounds and pence as a single decimal figure.
Mental zero-counting shortcuts break down when attention is split across several steps, and trailing zeros that are never written down cannot be counted back.
What to do instead
Work in the smallest whole unit for money questions (pence rather than pounds) and convert only at the end. For power-of-ten shifts, mark the decimal point position explicitly on paper at every step rather than moving it mentally.
Evaluates a mixed expression strictly left to right, so that 12 minus 3 times 2 is computed as 18 rather than 6.
Reading habits are left to right and linear, and expressions presented without brackets offer no visual cue that precedence applies.
What to do instead
Before calculating, circle every multiplication and division sign and resolve those operations first, rewriting the line after each one. Where a calculator is permitted, re-enter the expression with explicit brackets and check that the displayed answer matches the hand-worked sequence.
Compares bar heights or line slopes directly from a chart without checking where the axis begins, treating a bar that runs from 90 to 100 as twice the size of one that runs from 95 to 100.
The visual system judges length and gradient pre-attentively, and the axis labels sit at the edge of the figure where they are easy to skim past.
What to do instead
Read the axis start value and the unit of the scale before looking at any bar, and where the axis is truncated, compute the difference between the top and the baseline rather than judging the drawn length. State the two values numerically before comparing them.
Computes a percentage against the total budget when the question asks for a share of a named subset, or uses a gross figure where the question specifies net.
Qualifying words in the stem are short and sit close to words that look almost identical, so the distinction is lost during a fast first read.
What to do instead
Highlight or underline the qualifying phrase in the stem and cross out the columns or figures it rules out before doing any arithmetic. Write the chosen base figure on its own line with a one-word justification so the denominator is fixed before the division begins.