Example 3
This is a difficult example. It is immediately clear that there cannot be a monotonous or exponential relationship, because the numbers are not continuously increasing or decreasing. Check if the same transformation is applied between number 1 and number 2 as between number 3 and number 4 or number 4 and number 5. The transformation is *2 every other step.
The other pattern is more difficult to find. Since the step from -18 to -15 will in principle not be a multiplication, it is clear that the additional arches must be drawn.
The second series does not always have the same transformation. First + 3, then +6, then +9. So the answer is -39.
Tip: If a question contains more than 5 numbers, the chances of one of the more difficult patterns are higher. You don't have to look for these kinds of difficult patterns if only 4 numbers are given.