Numerical aptitude tests are used by employers because many jobs require you to work with numbers at least some of the time. Obviously, if you are applying for a job which involves working with numbers on a day-to-day basis, then the employer will regard your numerical aptitude as a valuable predictor of your performance on the job.
Numerical aptitude test questions range from simple arithmetic operations like addition and subtraction to more complex questions where you need to interpret numerical information presented as tables, diagrams, and graphs.
Tests from different suppliers vary in both the number and difficulty of the questions that they contain and there are several hundred of these tests on the market. The duration of any test you are asked to take will depend on several factors including how many other tests you are taking on the day. However, most tests last about 30-40 minutes and have about 30-40 questions.
The questions used in numerical aptitude tests can be classified into four basic types: numerical computation, numerical reasoning, data interpretation and numerical estimation.
Numerical computation questions involve the basic principles of arithmetic including: addition, subtraction, multiplication, division, percentages, ratios, fractions and decimals. To score well on these questions you will need to be able to make quick and accurate calculations without using a calculator.
Numerical reasoning questions test your reasoning ability rather than your ability to do calculations. This may include number series questions where you need to work out which number or numbers are missing from the series. They also include text based questions where a mathematical problem is posed in words and your task is to apply the necessary logic to find the answer.
Data interpretation questions commonly use: pie charts, line graphs, scatter-plots and tables of data which you need to interpret. The more complex questions may show the data in one format, for example a table, and a subset of this data in another format, for example a pie chart. To answer the questions you need to be able to cross reference these two elements in a logical way. These questions are widely used when selecting candidates for management and supervisory jobs where you are required to interpret data presented in charts, tables and graphs in order to make day-to-day decisions.
Numerical estimation questions require you to make quick estimates of the answers to straightforward numerical questions. You do not have time to actually calculate these answers because this will take up too much time and prevent you from answering enough questions to get a good score. Numerical estimation is key in many technical jobs where you need to quickly and accurately make estimates of material quantities etc.
Numerical aptitude tests can be divided into tests of simple numerical ability, where it is obvious which arithmetic operations you need to apply, and numerical reasoning tests where you are presented with data and questions but the method required to answer the questions is not obvious. In all cases you need to prepare by practicing your mental arithmetic until you are both quick and confident. Your score in the simple speed tests will be very much influenced by your aptitude to add, subtract, multiply and divide quickly and accurately.