Fluid intelligence is associated with handling relatively unfamiliar problems. Crystallized intelligence concerns acquired knowledge and skills. The distinction helps explain why solving a new pattern and answering a vocabulary question are not identical tasks.
Compare two examples
If you are asked what a familiar word means, stored knowledge is central. If you are shown an unfamiliar arrangement of shapes and asked to discover its rule, you need to infer a relationship from the information provided.
Neither task takes place in a vacuum. Reading the instructions uses learned language. Recognizing that a sequence might alternate uses previous experience. A puzzle can emphasize novel reasoning without being completely independent of knowledge.
Why practice changes the experience
The first time you encounter an interleaved sequence, noticing two separate patterns can be the main challenge. After several examples, you may test that possibility quickly. The format has become more familiar.
That is useful learning, but it complicates an interpretation that every score increase represents a change in a broad underlying ability. The task you face psychologically is no longer as unfamiliar as it was.
Avoid ranking the two as good and bad
Acquired knowledge is not merely rote memory, and novel reasoning is not the only valuable kind of thinking. Understanding a technical subject can require both a foundation of knowledge and the ability to apply it to a new case.
For example, interpreting an unfamiliar graph requires knowing what its axes mean, then reasoning about the relationships shown. The knowledge and the reasoning work together.
Use the distinction in practice
When reviewing an error, ask whether you lacked a concept or failed to apply information already available. If percentages were unfamiliar, learn that concept. If you understood percentages but used the wrong base, practice identifying the reference quantity.
This leads to a more specific learning plan than labeling yourself a fluid thinker or a knowledge-based thinker after a short online test.