Most wrong answers in numerical tests come from small slips, not hard maths. Here is where the slips happen and how to stop them, with worked examples.
Marks are usually lost on units, percentage direction and misread tables rather than on difficult arithmetic. Estimate first, read the question twice, and write down what the answer must look like before you calculate. Short, regular practice on timed sets beats a long cram.
Looking at the mistakes people make on practice sets, the same few patterns come up again and again. None of them need advanced maths to fix.
Keep a small error log while you practise. After each timed set, write one line for every wrong answer saying which of these four it was. After two or three sets you will see which one is yours, and that is where to focus.
Rounding is the cheapest accuracy check you have. Round the numbers to something friendly, work out an approximate answer, and then compare it with the options. Often two or three options can be dismissed without any exact calculation.
When the options are close, such as 76.9 and 77.1, estimation will not separate them and you need exact working. Spot that early by glancing at the spread of the options before you start.
Three percentage ideas cover the majority of questions. Each has a clean method.
Every figure above was checked with a short script before it went on this page, and you should do the same with your own practice questions: re-do the arithmetic a second way, for example by multiplying back, before you trust an answer.
A table can be read correctly and still produce a wrong answer if you answer a different question from the one asked. A routine helps.
The same discipline applies to charts, which has its own page in this series: data interpretation tips.
Unit questions look easy and still catch people, because the slip is a single wrong step in a chain. Write the unit next to every number as you go, and cancel units the way you cancel fractions.
Numerical tests normally give you an average of one to two minutes per question, though the exact limit depends on the test, so check the instructions in your invitation. The principle is the same everywhere. A question you cannot start within about twenty seconds is a candidate for skipping, if the test lets you move on, or for a quick estimate and educated guess if it does not.
When practising, time yourself honestly and finish sets even when you are stuck. Afterwards, redo the ones you missed untimed and look at the method, not just the answer. That second pass is where improvement comes from.
Use a calculator only if your test allows one. Many do, many do not, and the formats differ, so read numerical reasoning test formats to see what to expect.
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For a timed set before you start, the free numerical reasoning practice test has 10 original questions with explanations.
Use ReasonEra to build the skill, but a real assessment usually comes with its own conditions on outside help, so ask the recruiter if anything is unclear.
Unit and base errors are the most common, such as mixing thousands with millions or taking a percentage of the wrong number. Writing the unit beside each figure removes many of them.
Estimate first and calculate exactly only when the options are close together. Estimation saves time and also catches decimal-place slips.
Drill three types: percentage change, reverse percentage and percentage points. Do ten of each, then check every answer by working it back the other way.
It depends on the test and employer, so check your invitation. Practise both with and without one if you are not sure.
Fifteen to thirty minutes of timed practice with a review of errors is usually more effective than one long session. Short and regular suits most people better.
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Notes. The guide summarises widely published practice, and details differ between employers and publishers. If something here is out of date, email info@reasonera.com.