Numerical intelligence: number series
A lot of IQ tests contain questions of the number series type. This type consists of a series of numbers to which you have to add the last one. The series is built using a certain system, meaning the numbers are not in a random order.
If you find out the system, you can derive the number that you have to enter. Usually you can choose from several answers. For example:
2 - 0 - 4 - 0 - 8 - 0 - ...
The correct answer is 16. The system in this series is that the zero is followed by a number twice as large as the number before the zero.
If you're up for an assessment that includes number series, practicing numerical reasoning can help you to improve your skills.
The number series system
If you want to come up with your own number series, you have to come up with a good system. It is a challenge to come up with wrong answers that are not too easy: they must be wrong, but also have to be (somewhat) believable.
If the answers deviate too much from the right answer, in the above example for instance 124, you can immediately see they are wrong. In that case the test question is too easy. The real issue is finding the right balance between difficult and easy.
Read more on another type of IQ test questions called syllogism, or take an IQ test.